[Core] Refactoring sampler and support prompt logprob for chunked prefill (#4309)

tests/samplers/test_logprobs.py

@@ -9,15 +9,26 @@ MODELS = ["facebook/opt-125m"]
 
 @pytest.mark.parametrize("model", MODELS)
 @pytest.mark.parametrize("dtype", ["half"])
+@pytest.mark.parametrize("chunked_prefill_token_size", [1, 4, 16, -1])
+@pytest.mark.parametrize("num_top_logprobs", [6])  # 32000 == vocab_size
 def test_get_prompt_logprobs(
     hf_runner,
     vllm_runner,
     model,
     dtype,
+    chunked_prefill_token_size: int,
+    num_top_logprobs: int,
     example_prompts,
 ):
+    max_num_seqs = 256
+    enable_chunked_prefill = False
+    max_num_batched_tokens = None
+    if chunked_prefill_token_size != -1:
+        enable_chunked_prefill = True
+        max_num_seqs = min(chunked_prefill_token_size, max_num_seqs)
+        max_num_batched_tokens = chunked_prefill_token_size
+
     max_tokens = 5
-    num_top_logprobs = 6
     hf_model = hf_runner(model, dtype=dtype)
     hf_logprobs = hf_model.generate_greedy_logprobs(
         example_prompts,
@@ -25,10 +36,17 @@ def test_get_prompt_logprobs(
     )
     del hf_model
 
-    vllm_model = vllm_runner(model, dtype=dtype, max_logprobs=num_top_logprobs)
+    vllm_model = vllm_runner(
+        model,
+        dtype=dtype,
+        max_logprobs=num_top_logprobs,
+        enable_chunked_prefill=enable_chunked_prefill,
+        max_num_batched_tokens=max_num_batched_tokens,
+        max_num_seqs=max_num_seqs,
+    )
     vllm_sampling_params = SamplingParams(max_tokens=max_tokens,
                                           logprobs=num_top_logprobs,
-                                          prompt_logprobs=5,
+                                          prompt_logprobs=num_top_logprobs,
                                           temperature=0.0)
     vllm_results = vllm_model.model.generate(
         example_prompts, sampling_params=vllm_sampling_params)
@@ -52,9 +70,18 @@ def test_get_prompt_logprobs(
             "The output text from the top logprob for each token position "
             "should be the same as the output text in the result.")
 
+        # The first prompt logprob is always None
+        assert result.prompt_logprobs[0] is None
+        for prompt_logprobs in result.prompt_logprobs[1:]:
+            # If the prompt token is not included in the top X
+            # logprob, it can return 1 more data
+            assert (len(prompt_logprobs) == num_top_logprobs
+                    or len(prompt_logprobs) == num_top_logprobs + 1)
+
     # Test whether prompt logprobs are consistent with HF
     for vllm_result, hf_logprob in zip(vllm_results, hf_logprobs):
         # Check prompt logprobs
+        # The first prompt logprob is always None, so we compare it from 1:.
         vllm_prompt_logprobs = vllm_result.prompt_logprobs[1:]
         for i, vllm_prompt_logprob_dict in enumerate(vllm_prompt_logprobs):
             for token_id, logprob in vllm_prompt_logprob_dict.items():
@@ -74,6 +101,17 @@ def test_get_prompt_logprobs(
                     "The token should be decoded by the time it is returned "
                     " to the user.")
 
+    # Test if prompt logprobs are correctly set.
+    for vllm_result in vllm_results:
+        token_ids = vllm_result.prompt_token_ids
+        prompt_logprobs = vllm_result.prompt_logprobs
+
+        # The first token doesn't have logprob.
+        assert prompt_logprobs[0] is None
+
+        for token_id, logprob_dict in zip(token_ids[1:], prompt_logprobs[1:]):
+            assert token_id in logprob_dict
+
 
 def test_max_logprobs():
     runner = VllmRunner("facebook/opt-125m", max_logprobs=1)

tests/samplers/test_sampler.py

@@ -8,6 +8,7 @@ import torch
 from transformers import GenerationConfig, GenerationMixin
 
 from vllm.model_executor.layers.sampler import Sampler
+from vllm.model_executor.sampling_metadata import SamplingMetadata
 from vllm.model_executor.utils import set_random_seed
 from vllm.sequence import SamplingParams, SequenceData, SequenceGroupMetadata
 from vllm.utils import Counter
@@ -54,6 +55,7 @@ def _do_sample(
     sampler: MockLogitsSampler,
     model_runner: ModelRunner,
     sampling_params: SamplingParams,
+    device: str,
 ):
     seq_group_metadata_list = []
     prompt_lens = []
@@ -68,9 +70,12 @@ def _do_sample(
             ))
         prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
 
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
+    sampling_metadata = SamplingMetadata.prepare(
+        seq_group_metadata_list,
+        prompt_lens,
+        subquery_lens=prompt_lens,
+        device=device,
+        pin_memory=model_runner.pin_memory)
     return sampler(logits=input_tensor, sampling_metadata=sampling_metadata)
 
 
@@ -85,7 +90,7 @@ def test_sampler_all_greedy(seed: int, device: str):
 
     sampling_params = SamplingParams(temperature=0)
     sampler_output = _do_sample(batch_size, fake_logits, sampler, model_runner,
-                                sampling_params)
+                                sampling_params, device)
     expected = torch.argmax(fake_logits, dim=-1)
     for i, sequence_output in enumerate(sampler_output):
         for nth_output in sequence_output.samples:
@@ -111,7 +116,7 @@ def test_sampler_all_random(seed: int, device: str):
         n=random.randint(1, 10),
     )
     sampler_output = _do_sample(batch_size, fake_logits, sampler, model_runner,
-                                sampling_params)
+                                sampling_params, device)
 
     for i, sequence_output in enumerate(sampler_output):
         for nth_output in sequence_output.samples:
@@ -137,7 +142,7 @@ def test_sampler_all_random_seed(seed: int, device: str):
         seed=random.randint(0, 10000),
     )
     sampler_output = _do_sample(batch_size, fake_logits, sampler, model_runner,
-                                sampling_params)
+                                sampling_params, device)
 
     for i, sequence_output in enumerate(sampler_output):
         for nth_output in sequence_output.samples:
@@ -160,10 +165,10 @@ def test_sampler_all_random_seed_deterministic(seed: int, device: str):
         seed=random.randint(0, 10000),
     )
     first_sampler_output = _do_sample(batch_size, fake_logits, sampler,
-                                      model_runner, sampling_params)
+                                      model_runner, sampling_params, device)
 
     second_sampler_output = _do_sample(batch_size, fake_logits, sampler,
-                                       model_runner, sampling_params)
+                                       model_runner, sampling_params, device)
 
     assert first_sampler_output == second_sampler_output
 
@@ -183,7 +188,8 @@ def test_sampler_all_beam(seed: int, device: str):
         best_of=2,
         use_beam_search=True,
     )
-    _do_sample(batch_size, fake_logits, sampler, model_runner, sampling_params)
+    _do_sample(batch_size, fake_logits, sampler, model_runner, sampling_params,
+               device)
     # no assertion here as I am not sure how to determine whether
     # the outputs are expected - in other words, this just tests
     # whether there are no exceptions in the sampler
@@ -443,10 +449,12 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
              "batch size")
 
         _, fake_logits, sampler, model_runner = _prepare_test(batch_size)
-        sampling_metadata = model_runner._prepare_sample(
+        sampling_metadata = SamplingMetadata.prepare(
             seq_group_metadata_list,
             prompt_lens=prompt_lens if prompt_lens else None,
-            subquery_lens=prompt_lens if prompt_lens else None)
+            subquery_lens=prompt_lens if prompt_lens else None,
+            device=device,
+            pin_memory=model_runner.pin_memory)
         # the logits tensor is modified in-place by the sampler
         _ = sampler(logits=fake_logits, sampling_metadata=sampling_metadata)
 
@@ -530,8 +538,12 @@ def test_sampler_mixed(seed: int, device: str):
         prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
 
     def test_sampling(model_runner: ModelRunner):
-        sampling_metadata = model_runner._prepare_sample(
-            seq_group_metadata_list, prompt_lens, subquery_lens=prompt_lens)
+        sampling_metadata = SamplingMetadata.prepare(
+            seq_group_metadata_list,
+            prompt_lens,
+            subquery_lens=prompt_lens,
+            device=device,
+            pin_memory=model_runner.pin_memory)
         sampler_output = sampler(logits=fake_logits,
                                  sampling_metadata=sampling_metadata)
 
@@ -627,9 +639,12 @@ def test_sampler_top_k_top_p(seed: int, device: str):
             ))
         prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
 
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
+    sampling_metadata = SamplingMetadata.prepare(
+        seq_group_metadata_list,
+        prompt_lens,
+        subquery_lens=prompt_lens,
+        device=device,
+        pin_memory=model_runner.pin_memory)
 
     sample_probs = None
 

tests/test_logits_processor.py

@@ -6,6 +6,7 @@ import pytest
 import torch
 
 from vllm.model_executor.layers.logits_processor import LogitsProcessor
+from vllm.model_executor.sampling_metadata import SamplingMetadata
 from vllm.model_executor.utils import set_random_seed
 from vllm.sequence import SamplingParams, SequenceData, SequenceGroupMetadata
 from vllm.worker.model_runner import ModelRunner
@@ -82,9 +83,12 @@ def test_logits_processors(seed: int, device: str):
             ))
         prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
 
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
+    sampling_metadata = SamplingMetadata.prepare(
+        seq_group_metadata_list,
+        prompt_lens,
+        subquery_lens=prompt_lens,
+        device=model_runner.device,
+        pin_memory=model_runner.pin_memory)
     logits_processor_output = logits_processor(
         embedding=None,
         hidden_states=input_tensor,

tests/worker/test_model_runner.py

@@ -2,6 +2,7 @@ import pytest
 import torch
 
 from vllm.config import ModelConfig, SchedulerConfig
+from vllm.model_executor.sampling_metadata import SamplingMetadata
 from vllm.sequence import SamplingParams, SequenceData, SequenceGroupMetadata
 from vllm.worker.model_runner import ModelRunner, _get_graph_batch_size
 
@@ -97,9 +98,12 @@ def test_prepare_prompt(batch_size):
     assert len(input_positions) == sum(prompt_lens)
     torch.testing.assert_close(input_tokens, input_positions)
 
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
+    sampling_metadata = SamplingMetadata.prepare(
+        seq_group_metadata_list,
+        prompt_lens,
+        subquery_lens=prompt_lens,
+        device=model_runner.device,
+        pin_memory=model_runner.pin_memory)
     assert len(input_tokens) == sum(prompt_lens)
     assert len(input_positions) == sum(prompt_lens)
     actual = sampling_metadata.selected_token_indices
@@ -195,9 +199,12 @@ def test_prepare_decode_cuda_graph(batch_size):
     for prompt_len in prompt_lens:
         expected_selected_token_indices.append(selected_token_start_idx)
         selected_token_start_idx += 1
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
+    sampling_metadata = SamplingMetadata.prepare(
+        seq_group_metadata_list,
+        prompt_lens,
+        subquery_lens=prompt_lens,
+        device=model_runner.device,
+        pin_memory=model_runner.pin_memory)
     actual = sampling_metadata.selected_token_indices
     expected = torch.tensor(expected_selected_token_indices,
                             device=actual.device,

vllm/core/scheduler.py

@@ -915,6 +915,20 @@ class Scheduler:
                 self.block_manager.get_common_computed_block_ids(
                     seq_group.get_seqs(status=SequenceStatus.RUNNING)))
 
+            do_sample = True
+            if seq_group.is_prefill():
+                seqs = seq_group.get_seqs()
+                # Prefill has only 1 sequence.
+                assert len(seqs) == 1
+                # In the next iteration, all prompt tokens are not computed.
+                # It means the prefill is chunked, and we don't need sampling.
+                # NOTE: We use get_len instead of get_prompt_len because when
+                # a sequence is preempted, prefill includes previous generated
+                # output tokens.
+                if (token_chunk_size + seqs[0].data.get_num_computed_tokens() <
+                        seqs[0].data.get_len()):
+                    do_sample = False
+
             # It assumes the scheduled_seq_groups is ordered by
             # prefill < decoding.
             is_prompt = seq_group.is_prefill()
@@ -924,6 +938,7 @@ class Scheduler:
                 seq_data=seq_data,
                 sampling_params=seq_group.sampling_params,
                 block_tables=block_tables,
+                do_sample=do_sample,
                 token_chunk_size=token_chunk_size,
                 lora_request=seq_group.lora_request,
                 computed_block_nums=common_computed_block_nums,

vllm/engine/async_llm_engine.py

@@ -219,7 +219,7 @@ class _AsyncLLMEngine(LLMEngine):
 
         request_outputs = self._process_model_outputs(
             output, scheduler_outputs.scheduled_seq_groups,
-            scheduler_outputs.ignored_seq_groups)
+            scheduler_outputs.ignored_seq_groups, seq_group_metadata_list)
 
         # Log stats.
         if self.log_stats:

vllm/engine/llm_engine.py

@@ -22,7 +22,7 @@ from vllm.lora.request import LoRARequest
 from vllm.outputs import RequestOutput
 from vllm.sampling_params import SamplingParams
 from vllm.sequence import (MultiModalData, SamplerOutput, Sequence,
-                           SequenceGroup, SequenceStage)
+                           SequenceGroup, SequenceGroupMetadata)
 from vllm.transformers_utils.detokenizer import Detokenizer
 from vllm.transformers_utils.tokenizer_group import (BaseTokenizerGroup,
                                                      get_tokenizer_group)
@@ -476,9 +476,12 @@ class LLMEngine:
         return self.scheduler.has_unfinished_seqs()
 
     def _process_model_outputs(
-            self, output: List[SamplerOutput],
-            scheduled_seq_groups: List[SequenceGroup],
-            ignored_seq_groups: List[SequenceGroup]) -> List[RequestOutput]:
+        self,
+        output: List[SamplerOutput],
+        scheduled_seq_groups: List[SequenceGroup],
+        ignored_seq_groups: List[SequenceGroup],
+        seq_group_metadata_list: List[SequenceGroupMetadata],
+    ) -> List[RequestOutput]:
         """Apply the model output to the sequences in the scheduled seq groups.
 
         Returns RequestOutputs that can be returned to the client.
@@ -492,17 +495,15 @@ class LLMEngine:
             sampler_outputs=output, num_seq_groups=len(scheduled_seq_groups))
 
         # Update the scheduled sequence groups with the model outputs.
-        for scheduled_seq_group, outputs in zip(scheduled_seq_groups,
-                                                output_by_sequence_group):
+        for scheduled_seq_group, outputs, seq_group_meta in zip(
+                scheduled_seq_groups, output_by_sequence_group,
+                seq_group_metadata_list):
             seq_group = scheduled_seq_group.seq_group
             seq_group.update_num_computed_tokens(
                 scheduled_seq_group.token_chunk_size)
 
-            # If all sequences in the sequence group are in DECODE, then we can
-            # process the output tokens. Otherwise, they are (chunked) prefill
-            # samples and should not be processed.
-            stages = [seq.data._stage for seq in seq_group.seqs_dict.values()]
-            if all(stage == SequenceStage.DECODE for stage in stages):
+            self.output_processor.process_prompt_logprob(seq_group, outputs)
+            if seq_group_meta.do_sample:
                 self.output_processor.process_outputs(seq_group, outputs)
 
         # Free the finished sequence groups.
@@ -585,7 +586,7 @@ class LLMEngine:
 
         request_outputs = self._process_model_outputs(
             output, scheduler_outputs.scheduled_seq_groups,
-            scheduler_outputs.ignored_seq_groups)
+            scheduler_outputs.ignored_seq_groups, seq_group_metadata_list)
 
         # Log stats.
         if self.log_stats:

vllm/engine/output_processor/interfaces.py

@@ -68,3 +68,9 @@ class SequenceGroupOutputProcessor(ABC):
         scheduler.
         """
         pass
+
+    @abstractmethod
+    def process_prompt_logprob(self, seq_group: SequenceGroup,
+                               outputs: List[SequenceGroupOutput]) -> None:
+        """Update prompt logprobs received from outputs to seq_group."""
+        pass

vllm/engine/output_processor/multi_step.py

@@ -44,6 +44,15 @@ class MultiStepOutputProcessor(SequenceGroupOutputProcessor):
         self.get_tokenizer_for_seq = get_tokenizer_for_seq
         self.stop_checker = stop_checker
 
+    def process_prompt_logprob(self, seq_group: SequenceGroup,
+                               outputs: List[SequenceGroupOutput]) -> None:
+        # TODO(sang): Prompt logprob currently not implemented in multi step
+        # workers.
+        logger.warning(
+            "Prompt logprob is not supported by multi step workers. "
+            "(e.g., speculative decode uses multi step workers).")
+        pass
+
     def process_outputs(self, sequence_group: SequenceGroup,
                         outputs: List[SequenceGroupOutput]) -> None:
         """Append new tokens in the outputs to sequences in the sequence group.

vllm/engine/output_processor/single_step.py

@@ -55,17 +55,23 @@ class SingleStepOutputProcessor(SequenceGroupOutputProcessor):
                 ), f"{type(self)} does not support multiple outputs per step"
         return self._process_sequence_group_outputs(sequence_group, outputs[0])
 
-    def _process_sequence_group_outputs(self, seq_group: SequenceGroup,
-                                        outputs: SequenceGroupOutput) -> None:
-
-        # Process prompt logprobs
-        prompt_logprobs = outputs.prompt_logprobs
-        if prompt_logprobs is not None and \
-            seq_group.sampling_params.detokenize and self.detokenizer:
+    def process_prompt_logprob(self, seq_group: SequenceGroup,
+                               outputs: List[SequenceGroupOutput]) -> None:
+        assert len(outputs) == 1, ("Single step should only has 1 output.")
+        output = outputs[0]
+        prompt_logprobs = output.prompt_logprobs
+        if (prompt_logprobs is not None
+                and seq_group.sampling_params.detokenize and self.detokenizer):
             self.detokenizer.decode_prompt_logprobs_inplace(
                 seq_group, prompt_logprobs)
-            seq_group.prompt_logprobs = prompt_logprobs
+            if not seq_group.prompt_logprobs:
+                # The first prompt token's logprob is None because it doesn't
+                # have tokens that are precedent.
+                seq_group.prompt_logprobs = [None]
+            seq_group.prompt_logprobs.extend(prompt_logprobs)
 
+    def _process_sequence_group_outputs(self, seq_group: SequenceGroup,
+                                        outputs: SequenceGroupOutput) -> None:
         # Process samples
         samples = outputs.samples
         parent_seqs = seq_group.get_seqs(status=SequenceStatus.RUNNING)

vllm/engine/output_processor/util.py

@@ -1,10 +1,11 @@
 from typing import List
 
-from vllm.sequence import SamplerOutput
+from vllm.sequence import SamplerOutput, SequenceGroupOutput
 
 
-def create_output_by_sequence_group(sampler_outputs: List[SamplerOutput],
-                                    num_seq_groups: int):
+def create_output_by_sequence_group(
+        sampler_outputs: List[SamplerOutput],
+        num_seq_groups: int) -> List[List[SequenceGroupOutput]]:
     """Helper method which transforms a 2d list organized by
     [step][sequence group] into [sequence group][step].
     """

vllm/model_executor/layers/logits_processor.py

@@ -83,30 +83,27 @@ def _apply_logits_processors(
     logits: torch.Tensor,
     sampling_metadata: SamplingMetadata,
 ) -> torch.Tensor:
-    logits_row_idx = 0
     found_logits_processors = False
-    for i, seq_group in enumerate(sampling_metadata.seq_groups):
-        seq_ids, sampling_params = seq_group
+    logits_processed = 0
+    for seq_group in sampling_metadata.seq_groups:
+        seq_ids = seq_group.seq_ids
+        sampling_params = seq_group.sampling_params
         logits_processors = sampling_params.logits_processors
-        # handle prompt_logprobs by skipping rows in logits added for
-        # the prompt tokens (prompt logprobs are not processed)
-        if (i < sampling_metadata.num_prompts
-                and sampling_params.prompt_logprobs is not None):
-            assert len(seq_ids) == 1
-            logits_row_idx += sampling_metadata.prompt_lens[i] - 1
 
         if logits_processors:
             found_logits_processors = True
-            for seq_id in seq_ids:
+            for seq_id, logits_row_idx in zip(seq_ids,
+                                              seq_group.sample_indices):
                 logits_row = logits[logits_row_idx]
-                token_ids = sampling_metadata.seq_data[seq_id].output_token_ids
+                token_ids = seq_group.seq_data[seq_id].output_token_ids
                 for logits_processor in logits_processors:
                     logits_row = logits_processor(token_ids, logits_row)
                 logits[logits_row_idx] = logits_row
-                logits_row_idx += 1
-        else:
-            logits_row_idx += len(seq_ids)
+
+        logits_processed += len(seq_group.sample_indices) + len(
+            seq_group.prompt_logprob_indices)
+
     if found_logits_processors:
         # verifies that no rows in logits were missed unexpectedly
-        assert logits_row_idx == logits.shape[0]
+        assert logits_processed == logits.shape[0]
     return logits

vllm/model_executor/layers/sampler.py

@@ -7,11 +7,11 @@ import torch.nn as nn
 
 from vllm.model_executor.layers.ops.sample import sample as sample_triton
 from vllm.model_executor.sampling_metadata import (SamplingMetadata,
-                                                   SamplingTensors)
-from vllm.sampling_params import SamplingParams, SamplingType
+                                                   SamplingTensors,
+                                                   SequenceGroupToSample)
+from vllm.sampling_params import SamplingType
 from vllm.sequence import (Logprob, PromptLogprobs, SampleLogprobs,
-                           SamplerOutput, SequenceData, SequenceGroupOutput,
-                           SequenceOutput)
+                           SamplerOutput, SequenceGroupOutput, SequenceOutput)
 
 
 class Sampler(nn.Module):
@@ -48,11 +48,14 @@ class Sampler(nn.Module):
         logits: torch.Tensor,
         sampling_metadata: SamplingMetadata,
     ) -> Optional[SamplerOutput]:
+        """
+        Args:
+            logits: (num_tokens, vocab_size).
+            sampling_metadata: Metadata for sampling.
+        """
         assert logits is not None
         _, vocab_size = logits.shape
 
-        # Apply min_tokens penalty which sets stop tokens to -inf if min_tokens
-        # have not been generated yet
         logits = _apply_min_tokens_penalty(logits, sampling_metadata)
 
         # Prepare sampling tensors with pinned memory to avoid blocking.
@@ -83,7 +86,6 @@ class Sampler(nn.Module):
         # Compute the probabilities.
         probs = torch.softmax(logits, dim=-1, dtype=torch.float)
         # Compute the log probabilities.
-        # Use log_softmax to ensure numerical stability.
         logprobs = torch.log_softmax(logits, dim=-1, dtype=torch.float)
 
         # Sample the next tokens.
@@ -149,24 +151,28 @@ def _apply_min_tokens_penalty(
     logits: torch.Tensor,
     sampling_metadata: SamplingMetadata,
 ) -> torch.Tensor:
+    """Apply min_tokens penalty which sets stop tokens to -inf if min_tokens
+        have not been generated yet
+    """
     # list of indices in logits that will be set to -inf
     logits_to_penalize = []
-    start_idx = 0
-    for i, seq_group in enumerate(sampling_metadata.seq_groups):
-        seq_ids, sampling_params = seq_group
+    logits_applied = 0
+    for seq_group in sampling_metadata.seq_groups:
+        seq_ids = seq_group.seq_ids
+        sampling_params = seq_group.sampling_params
 
-        # handle prompt_logprobs by skipping rows in logits added for the prompt
-        # tokens (prompt logprobs are not penalized)
-        if (i < sampling_metadata.num_prompts
-                and sampling_params.prompt_logprobs is not None):
-            assert len(seq_ids) == 1
-            start_idx += sampling_metadata.prompt_lens[i] - 1
+        sample_indices = seq_group.sample_indices
+        logits_applied += len(sample_indices) + len(
+            seq_group.prompt_logprob_indices)
+        if not seq_group.do_sample:
+            continue
 
+        start_idx = sample_indices[0]
         min_tokens = sampling_params.min_tokens
         if min_tokens > 0:
             seqs_to_penalize = []
             for i, seq_id in enumerate(seq_ids):
-                seq_data = sampling_metadata.seq_data[seq_id]
+                seq_data = seq_group.seq_data[seq_id]
                 if len(seq_data.output_token_ids) < min_tokens:
                     seqs_to_penalize.append(i)
 
@@ -180,15 +186,13 @@ def _apply_min_tokens_penalty(
                 logits_to_penalize.extend(
                     itertools.product(seqs_to_penalize, token_ids_to_penalize))
 
-        start_idx += len(seq_ids)
-
     if logits_to_penalize:
         # use zip and * to group indices along each dimension
         # eg. [ (1,2), (1,3), (5,6) ] -> ( (1,1,5), (2,3,6) )
         logits[tuple(zip(*logits_to_penalize))] = -float("inf")
 
     # verifies that no rows in logits were missed unexpectedly
-    assert start_idx == logits.shape[0]
+    assert logits_applied == logits.shape[0]
     return logits
 
 
@@ -265,14 +269,30 @@ def _apply_min_p(
 
 
 def _greedy_sample(
-    selected_seq_groups: List[Tuple[List[int], SamplingParams]],
+    selected_seq_groups: List[SequenceGroupToSample],
     samples: torch.Tensor,
 ) -> List[Tuple[List[int], List[int]]]:
+    """Run greedy sampling on a given samples.
+
+    Args:
+        selected_seq_groups: A list of sequence groups batched.
+        samples: (num_selected_samples,) A tensor of samples. The length of
+            samples could be smaller than selected_seq_groups if
+            seq_group.do_sample is False.
+    Returns:
+        Tuple of (next_token_ids, parent_ids). The length of returned list is
+        same as the length of selected_seq_groups. If the corresponding
+        seq_group has do_sample=False, tuple contains ([], [])
+    """
     samples = samples.tolist()
     sample_idx = 0
     results = []
     for seq_group in selected_seq_groups:
-        seq_ids, _ = seq_group
+        if not seq_group.do_sample:
+            results.append(([], []))
+            continue
+
+        seq_ids = seq_group.seq_ids
         num_parent_seqs = len(seq_ids)
         assert num_parent_seqs == 1, (
             "Greedy sampling should have only one seq.")
@@ -284,16 +304,33 @@ def _greedy_sample(
 
 
 def _random_sample(
-    selected_seq_groups: List[Tuple[List[int], SamplingParams]],
-    is_prompts: List[bool],
+    selected_seq_groups: List[SequenceGroupToSample],
     random_samples: torch.Tensor,
 ) -> List[Tuple[List[int], List[int]]]:
+    """Run random sampling on a given samples.
+
+    Args:
+        selected_seq_groups: A list of sequence groups batched.
+        random_samples: (num_selected_samples,) A tensor of samples. The
+            length of samples could be smaller than selected_seq_groups if
+            seq_group.do_sample is False.
+    Returns:
+        Tuple of (next_token_ids, parent_ids). The length of returned list is
+        same as the length of selected_seq_groups. If the corresponding
+        seq_group has do_sample=False, tuple contains ([], [])
+    """
     # Find the maximum best_of value of the prompt phase requests.
     random_samples = random_samples.cpu()
     sample_idx = 0
     results = []
-    for seq_group, is_prompt in zip(selected_seq_groups, is_prompts):
-        seq_ids, sampling_params = seq_group
+    for seq_group in selected_seq_groups:
+        if not seq_group.do_sample:
+            results.append(([], []))
+            continue
+
+        seq_ids = seq_group.seq_ids
+        sampling_params = seq_group.sampling_params
+        is_prompt = seq_group.is_prompt
         num_parent_seqs = len(seq_ids)
         if is_prompt:
             # Prompt phase.
@@ -311,11 +348,20 @@ def _random_sample(
 
 
 def _beam_search_sample(
-    selected_seq_groups: List[Tuple[List[int], SamplingParams]],
-    is_prompts: List[bool],
-    seq_data: Dict[int, SequenceData],
+    selected_seq_groups: List[SequenceGroupToSample],
     logprobs: torch.Tensor,
 ) -> List[Tuple[List[int], List[int]]]:
+    """Run beam sampling on a given samples.
+
+    Args:
+        selected_seq_groups: A list of sequence groups batched.
+        logprobs: (num_selected_samples, vocab_size,) A tensor of logprob
+        on selected sample indices.
+    Returns:
+        Tuple of (next_token_ids, parent_ids). The length of returned list is
+        same as the length of selected_seq_groups. If the corresponding
+        seq_group has do_sample=False, tuple contains ([], [])
+    """
     # We sample 2 * beam_width candidates to make sure that with high
     # probability we can get `beam_width` candidates in addition to
     # the finished sequences for the next iteration. See
@@ -327,8 +373,13 @@ def _beam_search_sample(
     # other sampling methods.
     sample_idx = 0
     results = []
-    for seq_group, is_prompt in zip(selected_seq_groups, is_prompts):
-        seq_ids, sampling_params = seq_group
+    for seq_group in selected_seq_groups:
+        if not seq_group.do_sample:
+            results.append(([], []))
+            continue
+
+        is_prompt = seq_group.is_prompt
+        seq_ids, sampling_params = seq_group.seq_ids, seq_group.sampling_params
         num_parent_seqs = len(seq_ids)
         beam_width = sampling_params.best_of
         seq_group_logprobs = logprobs[sample_idx:sample_idx + num_parent_seqs]
@@ -343,7 +394,8 @@ def _beam_search_sample(
         else:
             # Generation phase.
             cumulative_logprobs = [
-                seq_data[seq_id].cumulative_logprob for seq_id in seq_ids
+                seq_group.seq_data[seq_id].cumulative_logprob
+                for seq_id in seq_ids
             ]
             cumulative_logprobs = torch.tensor(
                 cumulative_logprobs,
@@ -371,8 +423,7 @@ def _beam_search_sample(
 def _multinomial(
     probs: torch.Tensor,
     num_samples: int,
-    seq_groups: Optional[List[Tuple[List[int], SamplingParams]]] = None,
-    generators: Optional[List[torch.Generator]] = None,
+    seq_groups: Optional[List[SequenceGroupToSample]] = None,
 ) -> torch.Tensor:
     if num_samples > 1:
         # This is equivalent to torch.repeat_interleaved (which also
@@ -388,9 +439,11 @@ def _multinomial(
         q.exponential_()
     else:
         sample_idx = 0
-        for (seq_ids, _), generator in zip(seq_groups, generators):
+        for seq_group in seq_groups:
+            seq_ids = seq_group.seq_ids
             next_sample_idx = sample_idx + len(seq_ids) * num_samples
-            q[sample_idx:next_sample_idx].exponential_(generator=generator)
+            q[sample_idx:next_sample_idx].exponential_(
+                generator=seq_group.generator)
             sample_idx = next_sample_idx
     return probs.div_(q).argmax(dim=1).view(-1, num_samples)
 
@@ -405,7 +458,7 @@ def _sample_with_torch(
     categorized_seq_group_ids = {t: [] for t in SamplingType}
     categorized_sample_indices = sampling_metadata.categorized_sample_indices
     for i, seq_group in enumerate(sampling_metadata.seq_groups):
-        _, sampling_params = seq_group
+        sampling_params = seq_group.sampling_params
         sampling_type = sampling_params.sampling_type
         categorized_seq_group_ids[sampling_type].append(i)
 
@@ -429,13 +482,11 @@ def _sample_with_torch(
         num_tokens = len(sample_indices)
         if num_tokens == 0:
             continue
-        seq_group_ids = categorized_seq_group_ids[sampling_type]
-        seq_groups = [sampling_metadata.seq_groups[i] for i in seq_group_ids]
-        is_prompts = [i < sampling_metadata.num_prompts for i in seq_group_ids]
-        sample_metadata[sampling_type] = (seq_group_ids, seq_groups,
-                                          is_prompts, sample_indices)
-        long_sample_indices = sample_indices.long()
 
+        seq_group_id = categorized_seq_group_ids[sampling_type]
+        seq_groups = [sampling_metadata.seq_groups[i] for i in seq_group_id]
+        sample_metadata[sampling_type] = (seq_group_id, seq_groups)
+        long_sample_indices = sample_indices.long()
         if sampling_type == SamplingType.GREEDY:
             greedy_samples = torch.argmax(logprobs[long_sample_indices],
                                           dim=-1)
@@ -455,14 +506,13 @@ def _sample_with_torch(
 
         elif sampling_type in (SamplingType.RANDOM, SamplingType.RANDOM_SEED):
             max_best_of_in_batch = 1
-            for seq_group, is_prompt in zip(seq_groups, is_prompts):
-                if is_prompt:
-                    _, sampling_params = seq_group
+            for seq_group in seq_groups:
+                if seq_group.is_prompt:
+                    sampling_params = seq_group.sampling_params
                     max_best_of_in_batch = max(max_best_of_in_batch,
                                                sampling_params.best_of)
             seeded_args = {} if sampling_type == SamplingType.RANDOM else {
                 "seq_groups": seq_groups,
-                "generators": sampling_metadata.generators,
             }
 
             multinomial_samples[sampling_type] = _multinomial(
@@ -481,25 +531,22 @@ def _sample_with_torch(
 
     # GPU<->CPU sync happens in the loop below.
     # This also converts the sample output to Python objects.
-
     for sampling_type in SamplingType:
         if sampling_type not in sample_metadata:
             continue
-        seq_group_ids, seq_groups, is_prompts, sample_indices = sample_metadata[
-            sampling_type]
+        (seq_group_id, seq_groups) = sample_metadata[sampling_type]
         if sampling_type == SamplingType.GREEDY:
             sample_results = _greedy_sample(seq_groups, greedy_samples)
         elif sampling_type in (SamplingType.RANDOM, SamplingType.RANDOM_SEED):
-            sample_results = _random_sample(seq_groups, is_prompts,
+            sample_results = _random_sample(seq_groups,
                                             multinomial_samples[sampling_type])
         elif sampling_type == SamplingType.BEAM:
-            sample_results = _beam_search_sample(seq_groups, is_prompts,
-                                                 sampling_metadata.seq_data,
+            sample_results = _beam_search_sample(seq_groups,
                                                  beam_search_logprobs)
-        sample_results_dict.update(zip(seq_group_ids, sample_results))
+        sample_results_dict.update(zip(seq_group_id, sample_results))
 
     sample_results = [
-        sample_results_dict[i]
+        sample_results_dict.get(i, ([], []))
         for i in range(len(sampling_metadata.seq_groups))
     ]
     return sample_results, sampled_token_ids_tensor
@@ -514,7 +561,7 @@ def _sample_with_triton_kernel(
     categorized_seq_group_ids = {t: [] for t in SamplingType}
     categorized_sample_indices = sampling_metadata.categorized_sample_indices
     for i, seq_group in enumerate(sampling_metadata.seq_groups):
-        _, sampling_params = seq_group
+        sampling_params = seq_group.sampling_params
         sampling_type = sampling_params.sampling_type
         categorized_seq_group_ids[sampling_type].append(i)
 
@@ -530,17 +577,16 @@ def _sample_with_triton_kernel(
         num_tokens = len(sample_indices)
         if num_tokens == 0:
             continue
-        seq_group_ids = categorized_seq_group_ids[sampling_type]
-        seq_groups = [sampling_metadata.seq_groups[i] for i in seq_group_ids]
-        is_prompts = [i < sampling_metadata.num_prompts for i in seq_group_ids]
-        sample_metadata[sampling_type] = (seq_group_ids, seq_groups,
-                                          is_prompts, sample_indices,
+        seq_group_id = categorized_seq_group_ids[sampling_type]
+        seq_groups = [sampling_metadata.seq_groups[i] for i in seq_group_id]
+        sample_metadata[sampling_type] = (seq_group_id, seq_groups,
+                                          sample_indices,
                                           sampled_token_indices)
         if sampling_type in (SamplingType.GREEDY, SamplingType.RANDOM,
                              SamplingType.RANDOM_SEED):
-            for seq_group, is_prompt in zip(seq_groups, is_prompts):
-                if is_prompt:
-                    _, sampling_params = seq_group
+            for seq_group in seq_groups:
+                if seq_group.is_prompt:
+                    sampling_params = seq_group.sampling_params
                     max_best_of_in_batch = max(max_best_of_in_batch,
                                                sampling_params.best_of)
         elif sampling_type == SamplingType.BEAM:
@@ -564,22 +610,21 @@ def _sample_with_triton_kernel(
     for sampling_type in SamplingType:
         if sampling_type not in sample_metadata:
             continue
-        (seq_group_ids, seq_groups, is_prompts, sample_indices,
+        (seq_group_id, seq_groups, sample_indices,
          sampled_token_indices) = sample_metadata[sampling_type]
         if sampling_type == SamplingType.GREEDY:
             sample_results = _greedy_sample(
                 seq_groups, sampled_tokens[sampled_token_indices][:, 0])
         elif sampling_type in (SamplingType.RANDOM, SamplingType.RANDOM_SEED):
             sample_results = _random_sample(
-                seq_groups, is_prompts, sampled_tokens[sampled_token_indices])
+                seq_groups, sampled_tokens[sampled_token_indices])
         elif sampling_type == SamplingType.BEAM:
-            sample_results = _beam_search_sample(seq_groups, is_prompts,
-                                                 sampling_metadata.seq_data,
+            sample_results = _beam_search_sample(seq_groups,
                                                  beam_search_logprobs)
-        sample_results_dict.update(zip(seq_group_ids, sample_results))
+        sample_results_dict.update(zip(seq_group_id, sample_results))
 
     sample_results = [
-        sample_results_dict[i]
+        sample_results_dict.get(i, ([], []))
         for i in range(len(sampling_metadata.seq_groups))
     ]
     return sample_results
@@ -590,6 +635,18 @@ def _sample(
     sampling_metadata: SamplingMetadata, sampling_tensors: SamplingTensors,
     include_gpu_probs_tensor: bool, modify_greedy_probs: bool
 ) -> Tuple[List[Tuple[List[int], List[int]]], Optional[torch.Tensor]]:
+    """
+    Args:
+        probs: (num_query_tokens_in_batch, num_vocab)
+        logprobs: (num_query_tokens_in_batch, num_vocab)
+        sampling_metadata: The metadata for a batch for sampling.
+        sampling_tensors: Tensors that include sampling related metadata.
+
+    Returns:
+        (next_token_ids, parent_seq_ids) for each seq group in a batch.
+            If sampling is skipped, it returns ([], [])
+        sampled_token_ids_tensor: A tensor of sampled token ids.    
+    """
     return _sample_with_torch(
         probs,
         logprobs,
@@ -626,56 +683,97 @@ def _get_logprobs(
     logprobs: torch.Tensor,
     sampling_metadata: SamplingMetadata,
     sample_results: List[Tuple[List[int], List[int]]],
-) -> Tuple[List[Optional[List[Optional[Dict[int, float]]]]], List[List[Dict[
-        int, float]]]]:
-    # Prepare query indices
-    batched_logprobs_query_seq_indices: List[int] = []
-    batched_logprobs_query_token_indices: List[int] = []
-    # at least get one logprob for each token
+) -> Tuple[List[Optional[PromptLogprobs]], List[SampleLogprobs]]:
+    """Return sample lobprobs and prompt logprobs.
+
+    The logic consists of 3 parts.
+    - Select indices to compute logprob from, ranks of token ids, and
+        the top k token ids from logprobs.
+    - Compute prompt logprobs if required.
+    - Compute sample logprobs if required.
+
+    Args:
+        logprobs: (num_query_tokens_across_batch, num_vocab). Each query token's
+            logprob per vocab. Sequence groups' query tokens are batched in a
+            single flattened tensor. For example, assuming there are N
+            seq groups, it is sorted by prefill tokens for seq_group_1 (if
+            prompt logprob is enabled), decode tokens for seq_group_1 (if
+            sampling is required), prefill tokens for seq_group_2, ...
+        sampling_metadata: The sampling metadata.
+        sample_results: (num_seq_groups) The tuple of (next_token_ids,
+            parent_ids) for each sequence group. When beam search is enabled,
+            sample_results can contain different number of seq_ids from
+            sampling_metadata.seq_groups. It is because beam search creates
+            2 * BEAM_WIDTH number of samples (whereas there are only up to
+            BEAM_WIDTH number of seq_ids).
+
+    Returns:
+        A tuple of prompt and sample logprobs per sequence group in a batch.
+    """
+    # The index of query token to calculate logprobs. It includes both
+    # prompt and sample logprob indices.
+    query_indices: List[int] = []
+    # The next token ids to get the logprob value from.
+    next_token_ids: List[int] = []
+    # The largest requested number of logprobs. We find logprobs as many as the
+    # largest num logprobs in this API.
     largest_num_logprobs = 1
-    sample_idx = 0
-    for i, (seq_group, sample_result) in enumerate(
-            zip(sampling_metadata.seq_groups, sample_results)):
-        seq_ids, sampling_params = seq_group
-        next_token_ids, parent_ids = sample_result
-        num_parent_seqs = len(seq_ids)
-        if (i < sampling_metadata.num_prompts
+
+    # Select indices to compute logprob from, ranks of token ids, and the top
+    # k token ids from logprobs.
+    for (seq_group, sample_result) in zip(sampling_metadata.seq_groups,
+                                          sample_results):
+        sampling_params = seq_group.sampling_params
+
+        # Update indices and tokens for prompt logprobs.
+        if (seq_group.is_prompt
                 and sampling_params.prompt_logprobs is not None):
             largest_num_logprobs = max(largest_num_logprobs,
                                        sampling_params.prompt_logprobs)
-            prompt_len = sampling_metadata.prompt_lens[i]
-            prompt_tokens = sampling_metadata.seq_data[
-                seq_ids[0]].prompt_token_ids
-            batched_logprobs_query_seq_indices.extend(
-                sample_idx + j for j in range(prompt_len - 1))
-            batched_logprobs_query_token_indices.extend(
-                token_id for token_id in prompt_tokens[1:])
-            sample_idx += prompt_len - 1
-        batched_logprobs_query_seq_indices.extend(
-            [sample_idx + parent_id for parent_id in parent_ids])
-        batched_logprobs_query_token_indices.extend(next_token_ids)
-        if sampling_params.logprobs is not None:
-            largest_num_logprobs = max(largest_num_logprobs,
-                                       sampling_params.logprobs)
-        sample_idx += num_parent_seqs
-    assert sample_idx == logprobs.size(0)
+            next_prompt_tokens = _get_next_prompt_tokens(seq_group)
+            query_indices.extend(seq_group.prompt_logprob_indices)
+            next_token_ids.extend(next_prompt_tokens)
 
-    batched_logprobs_query_seq_indices_gpu = torch.tensor(
-        batched_logprobs_query_seq_indices, device=logprobs.device)
-    batched_logprobs_query_token_indices_gpu = torch.tensor(
-        batched_logprobs_query_token_indices, device=logprobs.device)
+        # Update indices and next tokenes for sample logprob.
+        if seq_group.do_sample:
+            token_ids, parent_seq_ids = sample_result
+            # NOTE: We cannot directly use sample_indices because
+            # sample_indices only contain parent seq_ids of a previous step.
+            # The current step may have different number of seq_ids, and
+            # we can obtain it from `sample_result[1]`.
+            query_idx = seq_group.sample_indices[0]
+            query_indices.extend(
+                [query_idx + parent_id for parent_id in parent_seq_ids])
+            next_token_ids.extend(token_ids)
 
-    # Batched query for logprobs of selected token
-    batched_logprobs_query_result = logprobs[[
-        batched_logprobs_query_seq_indices_gpu,
-        batched_logprobs_query_token_indices_gpu
+            if sampling_params.logprobs is not None:
+                largest_num_logprobs = max(largest_num_logprobs,
+                                           sampling_params.logprobs)
+
+        assert len(next_token_ids) == len(query_indices)
+
+    if len(query_indices) == 0:
+        empty_sampled_logprob = []
+        empty_prompt_logprob = None
+        return [empty_prompt_logprob], [empty_sampled_logprob]
+
+    query_indices_gpu = torch.tensor(query_indices, device=logprobs.device)
+    next_token_ids_gpu = torch.tensor(next_token_ids, device=logprobs.device)
+
+    # (num_selected_query_tokens, num_logprobs). Note that query_indices can
+    # contain duplicates if beam search is enabled.
+    selected_logprobs = logprobs[[
+        query_indices_gpu,
+        next_token_ids_gpu,
     ]]
+    ranks = _get_ranks(
+        logprobs[query_indices_gpu],
+        next_token_ids_gpu,
+    )
+    assert selected_logprobs.shape[0] == ranks.shape[0]
 
-    batched_ranks_query_result = _get_ranks(
-        logprobs[batched_logprobs_query_seq_indices_gpu],
-        batched_logprobs_query_token_indices_gpu)
-
-    # Batched query for logprobs of topk tokens
+    # Logprobs of topk tokens for a batch of sequence groups.
+    # (num_query_tokens_across_batch).
     if largest_num_logprobs > 0:
         top_logprobs, top_token_ids = torch.topk(logprobs,
                                                  largest_num_logprobs,
@@ -685,79 +783,136 @@ def _get_logprobs(
     else:
         top_logprobs, top_token_ids = None, None
 
-    batched_logprobs_query_result = batched_logprobs_query_result.cpu()
-    batched_ranks_query_result = batched_ranks_query_result.cpu()
+    selected_logprobs = selected_logprobs.cpu()
+    ranks = ranks.cpu()
 
-    # Gather results
-    result_prompt_logprobs: List[Optional[PromptLogprobs]] = []
-    result_sample_logprobs: List[SampleLogprobs] = []
-    sample_idx = 0
-    query_result_idx = 0
-    for i, (seq_group, sample_result) in enumerate(
-            zip(sampling_metadata.seq_groups, sample_results)):
-        seq_ids, sampling_params = seq_group
-        next_token_ids, parent_ids = sample_result
+    # Find prompt/sample logprobs.
+    prompt_logprobs_per_seq_group: List[Optional[PromptLogprobs]] = []
+    sample_logprobs_per_seq_group: List[SampleLogprobs] = []
+    top_logprob_idx = 0
+    selected_logprobs_idx = 0
 
-        # Prompt logprobs
-        if (i < sampling_metadata.num_prompts
-                and sampling_params.prompt_logprobs is not None):
-            num_logprobs = sampling_params.prompt_logprobs
-            prompt_tokens = sampling_metadata.seq_data[
-                seq_ids[0]].prompt_token_ids
-            group_prompt_logprobs: PromptLogprobs = [None]
-            for token_id in prompt_tokens[1:]:
-                prompt_logprobs_dict = {
-                    token_id:
-                    (batched_logprobs_query_result[query_result_idx].item(),
-                     batched_ranks_query_result[query_result_idx].item())
-                }
-                if num_logprobs > 0:
-                    prompt_logprobs_dict.update(
-                        zip(
-                            top_token_ids[sample_idx, :num_logprobs].tolist(),
-                            zip(
-                                top_logprobs[
-                                    sample_idx, :num_logprobs].tolist(),
-                                range(1, num_logprobs + 1))))
-                group_prompt_logprobs.append({
-                    token_id: Logprob(*logprob_rank)
-                    for token_id, logprob_rank in prompt_logprobs_dict.items()
-                })
-                sample_idx += 1
-                query_result_idx += 1
-            result_prompt_logprobs.append(group_prompt_logprobs)
-        else:
-            result_prompt_logprobs.append(None)
+    for seq_group, sample_result in zip(sampling_metadata.seq_groups,
+                                        sample_results):
+        (prompt_logprobs, top_logprob_idx,
+         selected_logprobs_idx) = _get_prompt_logprob_if_needed(
+             seq_group, selected_logprobs, ranks, top_token_ids, top_logprobs,
+             selected_logprobs_idx, top_logprob_idx)
+        prompt_logprobs_per_seq_group.append(prompt_logprobs)
 
-        # Sample logprobs
-        num_logprobs = sampling_params.logprobs
-        if num_logprobs is None:
-            num_logprobs = 0
-        group_sample_logprobs: SampleLogprobs = []
-        for next_token_id, parent_id in zip(next_token_ids, parent_ids):
-            sample_logprobs_dict = {
-                next_token_id:
-                (batched_logprobs_query_result[query_result_idx].item(),
-                 batched_ranks_query_result[query_result_idx].item())
+        (sampled_logprobs, top_logprob_idx,
+         selected_logprobs_idx) = _get_sampled_logprob_if_needed(
+             seq_group, sample_result, selected_logprobs, ranks, top_token_ids,
+             top_logprobs, selected_logprobs_idx, top_logprob_idx)
+        sample_logprobs_per_seq_group.append(sampled_logprobs)
+
+    return prompt_logprobs_per_seq_group, sample_logprobs_per_seq_group
+
+
+def _get_prompt_logprob_if_needed(
+    seq_group: SequenceGroupToSample,
+    selected_logprobs: torch.Tensor,
+    ranks: torch.Tensor,
+    top_token_ids: torch.Tensor,
+    top_logprobs: torch.Tensor,
+    selected_logprobs_idx: int,
+    top_logprob_idx: int,
+):
+    """Compute the prompt logprob from a sequence group if needed."""
+    sampling_params = seq_group.sampling_params
+    is_prompt = seq_group.is_prompt
+
+    # Find prompt logprobs
+    prompt_logprobs: Optional[PromptLogprobs] = None
+    if (is_prompt and sampling_params.prompt_logprobs is not None):
+        prompt_logprobs = []
+        num_logprobs = sampling_params.prompt_logprobs
+        next_prompt_tokens = _get_next_prompt_tokens(seq_group)
+        for token_id in next_prompt_tokens:
+            # Calculate the prompt logprob of the real prompt tokens.
+            # Use tuple here for performance (to use to_list()).
+            # {token_id: (logprob, rank_from_vocab)}
+            prompt_logprobs_dict: Dict[int, Tuple[float, int]] = {
+                token_id: (selected_logprobs[selected_logprobs_idx].item(),
+                           ranks[selected_logprobs_idx].item())
             }
-            query_result_idx += 1
-            if num_logprobs >= 0:
-                sample_logprobs_dict.update(
+
+            # Add top K prompt logprobs along with its rank.
+            if num_logprobs > 0:
+                prompt_logprobs_dict.update(
                     zip(
-                        top_token_ids[sample_idx +
+                        top_token_ids[top_logprob_idx, :num_logprobs].tolist(),
+                        zip(
+                            top_logprobs[
+                                top_logprob_idx, :num_logprobs].tolist(),
+                            # This is ranks. Since top_logprob is sorted,
+                            # we can just use a range here.
+                            range(1, num_logprobs + 1))))
+            prompt_logprobs.append({
+                token_id: Logprob(*logprob_and_rank)
+                for token_id, logprob_and_rank in prompt_logprobs_dict.items()
+            })
+            # + 1 to go to the next prompt token.
+            top_logprob_idx += 1
+            selected_logprobs_idx += 1
+    return prompt_logprobs, top_logprob_idx, selected_logprobs_idx
+
+
+def _get_sampled_logprob_if_needed(
+    seq_group: SequenceGroupToSample,
+    sample_result: Tuple[List[int], List[int]],
+    selected_logprobs: torch.Tensor,
+    ranks: torch.Tensor,
+    top_token_ids: torch.Tensor,
+    top_logprobs: torch.Tensor,
+    selected_logprobs_idx: int,
+    top_logprob_idx: int,
+):
+    """Compute the sample logprob if needed."""
+    seq_ids = seq_group.seq_ids
+    num_logprobs = seq_group.sampling_params.logprobs
+    if num_logprobs is None:
+        num_logprobs = 0
+    sampled_logprobs: SampleLogprobs = []
+    next_token_ids, parent_seq_ids = sample_result
+
+    if seq_group.do_sample:
+        assert len(next_token_ids) > 0
+        for (next_token_id, parent_id) in zip(next_token_ids, parent_seq_ids):
+            # Calculate the sample logprob of the real sampled tokens.
+            # Use tuple here for performance (to use to_list()).
+            # token_id: (logprob, rank_from_vocab)
+            sampled_logprobs_dict: Dict[int, Tuple[float, int]] = {
+                next_token_id:
+                (selected_logprobs[selected_logprobs_idx].item(),
+                 ranks[selected_logprobs_idx].item())
+            }
+            # +1 to go to the next sampled token. Note that
+            # selected_logprobs can contain duplicates unlike top_logprobs
+            # when beam search is enabled.
+            selected_logprobs_idx += 1
+
+            # Second, add top K logprobs along with its rank.
+            if num_logprobs >= 0:
+                sampled_logprobs_dict.update(
+                    zip(
+                        top_token_ids[top_logprob_idx +
                                       parent_id, :num_logprobs].tolist(),
                         zip(
-                            top_logprobs[sample_idx +
+                            top_logprobs[top_logprob_idx +
                                          parent_id, :num_logprobs].tolist(),
+                            # This is rank. Since top_logprob is sorted, we
+                            # can just use a range here.
                             range(1, num_logprobs + 1))))
-            group_sample_logprobs.append({
-                token_id: Logprob(*logprob_rank)
-                for token_id, logprob_rank in sample_logprobs_dict.items()
+            sampled_logprobs.append({
+                token_id: Logprob(*logprob_and_rank)
+                for token_id, logprob_and_rank in
+                sampled_logprobs_dict.items()
             })
-        result_sample_logprobs.append(group_sample_logprobs)
-        sample_idx += len(seq_ids)
-
-    return result_prompt_logprobs, result_sample_logprobs
+        # There are len(seq_ids) number of sampled tokens for the current
+        # sequence group in top_logprobs. Jump to the next seq_group.
+        top_logprob_idx += len(seq_ids)
+    return sampled_logprobs, top_logprob_idx, selected_logprobs_idx
 
 
 def _modify_greedy_probs_inplace(logprobs: torch.Tensor, probs: torch.Tensor,
@@ -832,7 +987,7 @@ def _build_sampler_output(
          group_sample_logprobs) in zip(sampling_metadata.seq_groups,
                                        sample_results, prompt_logprobs,
                                        sample_logprobs):
-        seq_ids, _ = seq_group
+        seq_ids = seq_group.seq_ids
         next_token_ids, parent_ids = sample_result
         seq_outputs = []
         for parent_id, next_token_id, logprobs in zip(parent_ids,
@@ -854,3 +1009,36 @@ def _build_sampler_output(
         sampled_token_probs=sampled_token_probs,
         sampled_token_ids=sampled_token_ids,
     )
+
+
+def _get_next_prompt_tokens(seq_group: SequenceGroupToSample) -> List[str]:
+    """Get a list of next prompt tokens to compute logprob from a
+        given sequence group.
+
+    It is used to compute prompt logprob. Imagine you have logprob for each
+    query token. Query token needs to know the next prompt token id to compute
+    prompt logprob. This is a helper to obtain next prompt token ids.
+
+    This API has to be used only when the caller knows seq_group is in prefill
+    stage.
+
+    Returns:
+        A list of next prompt tokens to compute logprob.
+    """
+    assert seq_group.is_prompt, (
+        "Caller should ensure the sequence group is in a prefill stage.")
+    seq_ids = seq_group.seq_ids
+    subquery_len = seq_group.subquery_len
+    assert subquery_len is not None
+    # prompt has only 1 seq id.
+    assert len(seq_ids) == 1
+    seq_data = seq_group.seq_data[seq_ids[0]]
+    computed_len = seq_data.get_num_computed_tokens()
+    prompt_tokens = seq_data.prompt_token_ids
+    # +1 because we are looking for a next prompt token.
+    next_token_index_start = computed_len + 1
+    next_token_index_end = min(computed_len + subquery_len + 1,
+                               len(prompt_tokens))
+    next_prompt_tokens = prompt_tokens[
+        next_token_index_start:next_token_index_end]
+    return next_prompt_tokens

vllm/model_executor/sampling_metadata.py

@@ -6,57 +6,275 @@ import torch
 
 from vllm.model_executor.layers.ops.sample import get_num_triton_sampler_splits
 from vllm.sampling_params import SamplingParams, SamplingType
-from vllm.sequence import SequenceData
-from vllm.utils import is_pin_memory_available
+from vllm.sequence import SequenceData, SequenceGroupMetadata
+from vllm.utils import (async_tensor_h2d, is_pin_memory_available,
+                        maybe_expand_dim)
 
 _SAMPLING_EPS = 1e-5
 _SEED_0_REPLACEMENT = 3403598558
 
 
+@dataclass
+class SequenceGroupToSample:
+    # Sequence ids for the sequence group in a previous step.
+    seq_ids: List[int]
+    sampling_params: SamplingParams
+    # seq_id -> sequence data.
+    seq_data: Dict[int, SequenceData]
+    # The length of the prompt of the sequence group. None if it is in a decode
+    # stage.
+    prompt_len: Optional[int]
+    # The length of the query tokens to compute in the current step. None if it
+    # is in a decode stage. The length of subquery_len <= prompt_len.
+    subquery_len: Optional[int]
+    # A random number generator for sampling.
+    generator: Optional[torch.Generator]
+    # True if the sequence group is in prefill stage. False if it is in a
+    # decode stage.
+    is_prompt: bool
+    # Query token indices from logits. to compute prompt logprob. Empty if
+    # prompt logprob is not required.
+    prompt_logprob_indices: List[int]
+    # Sample token indices from logits. Empty if sampling is not required.
+    sample_indices: List[int]
+
+    @property
+    def do_sample(self):
+        return len(self.sample_indices) > 0
+
+    def __post_init__(self):
+        if len(self.prompt_logprob_indices) > 0:
+            assert self.sampling_params.prompt_logprobs is not None
+        if self.is_prompt:
+            assert self.prompt_len is not None
+            assert self.subquery_len is not None
+
+
 class SamplingMetadata:
     """Metadata for input sequences. Used in sampler.
 
+    The usage is as follow;
+    ```
+    hidden_states = execute_model(...)
+    logits = hidden_states[sampling_metadata.selected_token_indices]
+    sample(logits)
+
+    def sample(logits):
+        # Use categorized_sample_indices for sampling....
+    ```
+
     Args:
-        seq_groups: List of (seq_ids, sampling_params).
-        seq_data: Seq_id -> SequenceData.
-        prompt_lens: Lengths of prompts.
-        selected_token_indices: Token indices selected for sampling.
+        seq_groups: List of batched sequence groups.
+        selected_token_indices: (num_query_tokens_to_logprob). Indices to find
+            logits from the initial model output hidden states.
         categorized_sample_indices: SamplingType -> token indices to sample.
-        generators: List of torch.Generators to use for seeded sampling
-        perform_sampling: Whether to perform sampling. This option is used to
-            make the sampling only happens in the driver worker, and disable
-            sampling in other worker processes.
+            Each token indices is 2D tensor of (num_indices, num_indices) where
+            the first item means the sample index within the returned logit
+            (before pruning padding), and the second item means the sample
+            index after pruning using selected_token_indices.
+            For example, if the returned logit is [1, 2, 3], and we select
+            [1, 2] for sampling, the pruned logit will be [2, 3]. In this case,
+            The first tuple is [1, 2] (sampled index within original logit),
+            and the second tuple is [0, 1] (sampled index within pruned logit).
+        num_prompts: Number of prompt sequence groups in seq_groups.
     """
 
     def __init__(
         self,
-        seq_groups: Optional[List[Tuple[List[int], SamplingParams]]],
-        seq_data: Optional[Dict[int, SequenceData]],
-        prompt_lens: Optional[List[int]],
+        seq_groups: List[SequenceGroupToSample],
         selected_token_indices: torch.Tensor,
-        categorized_sample_indices: Optional[Dict[SamplingType, torch.Tensor]],
-        generators: Optional[List[torch.Generator]] = None,
-        perform_sampling: bool = True,
+        categorized_sample_indices: Dict[SamplingType, torch.Tensor],
+        num_prompts: int,
     ) -> None:
         self.seq_groups = seq_groups
-        self.seq_data = seq_data
-        self.prompt_lens = prompt_lens
         self.selected_token_indices = selected_token_indices
         self.categorized_sample_indices = categorized_sample_indices
-        self.generators = generators
-        self.perform_sampling = perform_sampling
+        self.num_prompts = num_prompts
 
-        self.num_prompts = len(prompt_lens) if prompt_lens is not None else 0
+    @staticmethod
+    def prepare(
+        seq_group_metadata_list: List[SequenceGroupMetadata],
+        prompt_lens: List[int],
+        subquery_lens: Optional[List[int]],
+        device: str,
+        pin_memory: bool,
+    ) -> "SamplingMetadata":
+        (
+            seq_groups,
+            selected_token_indices,
+            categorized_sample_indices,
+            num_prompts,
+        ) = _prepare_seq_groups(seq_group_metadata_list, prompt_lens,
+                                subquery_lens, device)
+        selected_token_indices = async_tensor_h2d(selected_token_indices,
+                                                  dtype=torch.long,
+                                                  target_device=device,
+                                                  pin_memory=pin_memory)
+        categorized_sample_indices = {
+            t: maybe_expand_dim(
+                async_tensor_h2d(seq_ids,
+                                 dtype=torch.int,
+                                 target_device=device,
+                                 pin_memory=pin_memory), 2, 2)
+            for t, seq_ids in categorized_sample_indices.items()
+        }
+
+        sampling_metadata = SamplingMetadata(
+            seq_groups=seq_groups,
+            selected_token_indices=selected_token_indices,
+            categorized_sample_indices=categorized_sample_indices,
+            num_prompts=num_prompts,
+        )
+        return sampling_metadata
 
     def __repr__(self) -> str:
         return (
             "SamplingMetadata("
             f"seq_groups={self.seq_groups}, "
-            f"seq_data={self.seq_data}, "
-            f"prompt_lens={self.prompt_lens}, "
             f"selected_token_indices={self.selected_token_indices}, "
-            f"categorized_sample_indices={self.categorized_sample_indices}), "
-            f"perform_sampling={self.perform_sampling})")
+            f"categorized_sample_indices={self.categorized_sample_indices}), ")
+
+
+def _prepare_seq_groups(
+    seq_group_metadata_list: List[SequenceGroupMetadata],
+    prompt_lens: List[int],
+    subquery_lens: Optional[List[int]],
+    device: str,
+) -> Tuple[List[SequenceGroupToSample], List[int], Dict[
+        SamplingType, List[Tuple[int, int]]], int]:
+    """Prepare sequence groups and indices for sampling.
+
+    Args:
+        seq_group_metadata_list: A list of sequence group to batch.
+        prompt_lens: A list of prompt lens per sequence group.
+            Index of prompt len should match with seq_group_metadata_list.
+        subquery_lens: A list of query lengths. Prompt lens include the length
+            of entire prompt tokens, and it could be shorter.
+        device: A device to use for random number generator,
+            `SequenceGroupToSample.generator`.
+
+    Returns:
+        seq_groups: A list of sequence group to sample.
+        selected_token_indices: See the definition from `SamplingMetadata`.
+        categorized_sample_indices: See the definition from `SamplingMetadata`.
+        num_prompts: Total number of prompts from `seq_group_metadata_list`.
+    """
+    # Batched sequence groups for the current model forward stsep.
+    seq_groups: List[SequenceGroupToSample] = []
+    # A list of token indices to sample/compute logprob. It is used to
+    # prune the outcome logits from the model for the performance.
+    selected_token_indices: List[int] = []
+    # Used for selected_token_indices.
+    model_output_idx = 0
+
+    # Sampling type -> (
+    # indices to sample/prompt logprob within pruned output logits,
+    # indices to sample within pruned logits)
+    categorized_sample_indices: Dict[SamplingType, List[Tuple[int, int]]] = {
+        t: []
+        for t in SamplingType
+    }
+    # Index of logits to compute logprob. Logits include both prompt logprob
+    # and sample logprob indices.
+    logit_idx = 0
+    # Index to sample from a sample tensor. It is used by triton sample kernel.
+    # See `_sample_with_triton_kernel` for more details.
+    sample_idx = 0
+    # Total number of prompts from given sequence groups.
+    num_prompts = 0
+
+    for i, seq_group_metadata in enumerate(seq_group_metadata_list):
+        seq_ids = list(seq_group_metadata.seq_data.keys())
+        sampling_params = seq_group_metadata.sampling_params
+        is_prompt = seq_group_metadata.is_prompt
+        generator: Optional[torch.Generator] = None
+        # If the current seq group is in decode stage, it is None.
+        prompt_len: Optional[int] = None
+        subquery_len: Optional[int] = None
+        prompt_logprob_indices: List[int] = []
+        sample_indices: List[int] = []
+        do_sample = seq_group_metadata.do_sample
+
+        if seq_group_metadata.is_prompt:
+            if sampling_params.seed is not None:
+                seq_group_metadata.state.generator = torch.Generator(
+                    device=device).manual_seed(sampling_params.seed)
+
+            num_prompts += 1
+            num_prefill_sample = len(seq_ids)
+            assert num_prefill_sample == 1
+            assert subquery_lens is not None and prompt_lens is not None
+            subquery_len, prompt_len = subquery_lens[i], prompt_lens[i]
+            # If we need sampling, exclude num_prefill_sample tokens from
+            # prompt logprob.
+            prompt_logprob_len = (subquery_len - num_prefill_sample
+                                  if do_sample else subquery_len)
+            sample_len = num_prefill_sample if do_sample else 0
+        else:
+            # Decode
+            prompt_logprob_len = 0
+            sample_len = len(seq_ids) if do_sample else 0
+
+        # Update indices to select from the model output.
+        """
+        This blocks computes selected_token_indices which is used in the
+        following way.
+
+        hidden_states = model(...)
+        logits = hidden_states[selected_token_indices]
+        """
+
+        if sampling_params.prompt_logprobs:
+            selected_token_indices.extend(
+                range(model_output_idx, model_output_idx + prompt_logprob_len))
+        model_output_idx += prompt_logprob_len
+        if do_sample:
+            selected_token_indices.extend(
+                range(model_output_idx, model_output_idx + sample_len))
+        model_output_idx += sample_len
+
+        # We now find indices for logprob computation and sampling.
+        """
+        This block computes categorized_sample_indices which is used in the
+        following way.
+
+        hidden_states = model(...)
+        logits = hidden_states[selected_token_indices]
+        def sample(logits):
+           # Use categorized_sample_indices for sampling.
+           # prompt_logprob_indices to find prompt logprob indices.
+           # sample_indices to find sample indices.
+        """
+
+        if sampling_params.prompt_logprobs is not None:
+            prompt_logprob_indices.extend(
+                range(logit_idx, logit_idx + prompt_logprob_len))
+            logit_idx += prompt_logprob_len
+        if do_sample:
+            sample_indices.extend(range(logit_idx, logit_idx + sample_len))
+            categorized_sample_indices[sampling_params.sampling_type].extend(
+                list(
+                    zip(range(logit_idx, logit_idx + sample_len),
+                        range(sample_idx, sample_idx + sample_len))))
+            logit_idx += sample_len
+            sample_idx += sample_len
+
+        if sampling_params.seed is not None:
+            generator = seq_group_metadata.state.generator
+
+        seq_groups.append(
+            SequenceGroupToSample(
+                seq_ids=seq_ids,
+                sampling_params=sampling_params,
+                seq_data=seq_group_metadata.seq_data,
+                prompt_len=prompt_len,
+                subquery_len=subquery_len,
+                generator=generator,
+                is_prompt=is_prompt,
+                prompt_logprob_indices=list(prompt_logprob_indices),
+                sample_indices=list(sample_indices)))
+    return (seq_groups, selected_token_indices, categorized_sample_indices,
+            num_prompts)
 
 
 @dataclass
@@ -112,11 +330,10 @@ class SamplingTensors:
         seeds_to_generate = (extra_seeds_to_generate +
                              get_num_triton_sampler_splits(vocab_size))
 
-        sample_indices_start_idx = 0
         assert sampling_metadata.seq_groups is not None
-        assert sampling_metadata.seq_data is not None
-        for i, seq_group in enumerate(sampling_metadata.seq_groups):
-            seq_ids, sampling_params = seq_group
+        for seq_group in sampling_metadata.seq_groups:
+            seq_ids = seq_group.seq_ids
+            sampling_params = seq_group.sampling_params
             temperature = sampling_params.temperature
             p = sampling_params.presence_penalty
             f = sampling_params.frequency_penalty
@@ -145,45 +362,46 @@ class SamplingTensors:
                                      or abs(r - 1.0) >= _SAMPLING_EPS):
                 do_penalties = True
 
-            if (i < sampling_metadata.num_prompts
+            is_prompt = seq_group.is_prompt
+            if (seq_group.is_prompt
                     and sampling_params.prompt_logprobs is not None):
                 # For tokens in the prompt that we only need to get
                 # their logprobs
-                assert sampling_metadata.prompt_lens is not None
-                prompt_len = sampling_metadata.prompt_lens[i]
-                temperatures += [temperature] * (prompt_len - 1)
-                top_ps += [top_p] * (prompt_len - 1)
-                top_ks += [top_k] * (prompt_len - 1)
-                min_ps += [min_p] * (prompt_len - 1)
-                presence_penalties += [0] * (prompt_len - 1)
-                frequency_penalties += [0] * (prompt_len - 1)
-                repetition_penalties += [1] * (prompt_len - 1)
-                prompt_tokens.extend([] for _ in range(prompt_len - 1))
-                output_tokens.extend([] for _ in range(prompt_len - 1))
-            for seq_id in seq_ids:
-                seq_data = sampling_metadata.seq_data[seq_id]
-                prompt_tokens.append(seq_data.prompt_token_ids)
-                output_tokens.append(seq_data.output_token_ids)
-            temperatures += [temperature] * len(seq_ids)
-            top_ps += [top_p] * len(seq_ids)
-            top_ks += [top_k] * len(seq_ids)
-            min_ps += [min_p] * len(seq_ids)
-            presence_penalties += [p] * len(seq_ids)
-            frequency_penalties += [f] * len(seq_ids)
-            repetition_penalties += [r] * len(seq_ids)
+                subquery_len = seq_group.subquery_len
+                assert subquery_len is not None
+                prefill_len = len(seq_group.prompt_logprob_indices)
+                temperatures += [temperature] * prefill_len
+                top_ps += [top_p] * prefill_len
+                top_ks += [top_k] * prefill_len
+                min_ps += [min_p] * prefill_len
+                presence_penalties += [0] * prefill_len
+                frequency_penalties += [0] * prefill_len
+                repetition_penalties += [1] * prefill_len
+                prompt_tokens.extend([] for _ in range(prefill_len))
+                output_tokens.extend([] for _ in range(prefill_len))
+
+            if seq_group.do_sample:
+                sample_lens = len(seq_group.sample_indices)
+                assert sample_lens == len(seq_ids)
+                for seq_id in seq_ids:
+                    seq_data = seq_group.seq_data[seq_id]
+                    prompt_tokens.append(seq_data.prompt_token_ids)
+                    output_tokens.append(seq_data.output_token_ids)
+                temperatures += [temperature] * len(seq_ids)
+                top_ps += [top_p] * len(seq_ids)
+                top_ks += [top_k] * len(seq_ids)
+                min_ps += [min_p] * len(seq_ids)
+                presence_penalties += [p] * len(seq_ids)
+                frequency_penalties += [f] * len(seq_ids)
+                repetition_penalties += [r] * len(seq_ids)
 
-            is_prompt = i < sampling_metadata.num_prompts
             if is_prompt:
                 prompt_best_of.append(sampling_params.best_of)
-                assert sampling_metadata.prompt_lens is not None
-                prompt_len = sampling_metadata.prompt_lens[i]
+                subquery_len = seq_group.subquery_len
+                assert subquery_len is not None
 
-                if sampling_params.prompt_logprobs is not None:
-                    # NOTE: the sampling position is the last token
-                    # in the prompt
-                    sample_indices_start_idx += prompt_len - 1
             for seq_id in seq_ids:
-                seq_data = sampling_metadata.seq_data[seq_id]
+                seq_data = seq_group.seq_data[seq_id]
                 extra_entropy = extra_entropy or ()
                 seq_seeds = cls._get_sequence_seeds(
                     seed,
@@ -193,8 +411,7 @@ class SamplingTensors:
                     seeds_to_generate=seeds_to_generate,
                     is_greedy=is_greedy)
                 sampling_seeds.append(seq_seeds)
-                sample_indices.append(sample_indices_start_idx)
-                sample_indices_start_idx += 1
+            sample_indices.extend(seq_group.sample_indices)
 
         sampling_tensors = SamplingTensors.from_lists(
             temperatures, top_ps, top_ks, min_ps, presence_penalties,
@@ -217,12 +434,14 @@ class SamplingTensors:
         # Note that the performance will be very bad without
         # pinned memory.
         pin_memory = is_pin_memory_available()
-        prompt_max_len = max(len(tokens) for tokens in prompt_tokens)
+        prompt_max_len = max([len(tokens) for tokens in prompt_tokens],
+                             default=0)
         prompt_padded_tokens = [
             tokens + [vocab_size] * (prompt_max_len - len(tokens))
             for tokens in prompt_tokens
         ]
-        output_max_len = max(len(tokens) for tokens in output_tokens)
+        output_max_len = max([len(tokens) for tokens in output_tokens],
+                             default=0)
         output_padded_tokens = [
             tokens + [vocab_size] * (output_max_len - len(tokens))
             for tokens in output_tokens

vllm/sequence.py

@@ -28,7 +28,10 @@ class Logprob:
     decoded_token: Optional[str] = None
 
 
+# {token_id -> logprob} per each sequence group. None if the corresponding
+# sequence group doesn't require prompt logprob.
 PromptLogprobs = List[Optional[Dict[int, Logprob]]]
+# {token_id -> logprob} for each sequence group.
 SampleLogprobs = List[Dict[int, Logprob]]
 
 
@@ -215,7 +218,7 @@ class Sequence:
         self.eos_token_id = eos_token_id
         self.lora_request = lora_request
 
-        self.data = SequenceData(prompt_token_ids)
+        self.data: SequenceData = SequenceData(prompt_token_ids)
         self.output_logprobs: SampleLogprobs = []
         self.output_text = ""
 
@@ -559,6 +562,9 @@ class SequenceGroupMetadata:
         sampling_params: The sampling parameters used to generate the outputs.
         block_tables: The block tables. (Seq id -> list of physical block
             numbers)
+        do_sample: True if sampling is required. Sampling is not required when
+            e.g., prefill is chunked, and the current iteration only computes
+            query tokens for prefill, we don't need sampling.
         token_chunk_size: The number of tokens to be processed (per sequence).
             None if chunking is not required.
         state: Internal state tied to this sequence group.
@@ -573,6 +579,7 @@ class SequenceGroupMetadata:
         seq_data: Dict[int, SequenceData],
         sampling_params: SamplingParams,
         block_tables: Dict[int, List[int]],
+        do_sample: bool = True,
         token_chunk_size: Optional[int] = None,
         lora_request: Optional[LoRARequest] = None,
         computed_block_nums: Optional[List[int]] = None,
@@ -589,6 +596,7 @@ class SequenceGroupMetadata:
         self.multi_modal_data = multi_modal_data
         self.state = SequenceGroupState() if state is None else state
         self._token_chunk_size = token_chunk_size
+        self.do_sample = do_sample
 
         if self._token_chunk_size is None:
             if is_prompt:
@@ -650,6 +658,7 @@ class SequenceGroupOutput:
         prompt_logprobs: Optional[PromptLogprobs],
     ) -> None:
         self.samples = samples
+        # Prompt logprob for each prompt query token.
         self.prompt_logprobs = prompt_logprobs
 
     def __repr__(self) -> str:

vllm/worker/cpu_model_runner.py

@@ -1,4 +1,4 @@
-from typing import Dict, List, Optional, Tuple
+from typing import List, Optional, Tuple
 
 import torch
 from torch import nn
@@ -10,9 +10,8 @@ from vllm.distributed import broadcast_tensor_dict
 from vllm.logger import init_logger
 from vllm.model_executor import SamplingMetadata
 from vllm.model_executor.model_loader import get_model
-from vllm.sampling_params import SamplingParams, SamplingType
-from vllm.sequence import SamplerOutput, SequenceData, SequenceGroupMetadata
-from vllm.utils import make_tensor_with_pad, maybe_expand_dim
+from vllm.sequence import SamplerOutput, SequenceGroupMetadata
+from vllm.utils import make_tensor_with_pad
 
 logger = init_logger(__name__)
 
@@ -38,6 +37,8 @@ class CPUModelRunner:
         self.model_config = model_config
         self.parallel_config = parallel_config
         self.scheduler_config = scheduler_config
+        # Currently, CPU worker doesn't support chunked prefill.
+        assert self.scheduler_config.chunked_prefill_enabled is False
         self.lora_config = lora_config
         self.vision_language_config = vision_language_config
         self.load_config = load_config
@@ -252,99 +253,6 @@ class CPUModelRunner:
             attn_metadata,
         )
 
-    def _prepare_sample(
-        self,
-        seq_group_metadata_list: List[SequenceGroupMetadata],
-        prompt_lens: List[int],
-    ) -> SamplingMetadata:
-        seq_groups: List[Tuple[List[int], SamplingParams]] = []
-        selected_token_indices: List[int] = []
-        generators: List[torch.Generator] = []
-        selected_token_start_idx = 0
-        categorized_sample_indices: Dict[SamplingType,
-                                         List[Tuple[int, int]]] = {
-                                             t: []
-                                             for t in SamplingType
-                                         }
-        categorized_sample_indices_start_idx = 0
-        categorized_sampled_token_indices_start_idx = 0
-
-        for i, seq_group_metadata in enumerate(seq_group_metadata_list):
-            seq_ids = list(seq_group_metadata.seq_data.keys())
-            sampling_params = seq_group_metadata.sampling_params
-            seq_groups.append((seq_ids, sampling_params))
-
-            if seq_group_metadata.is_prompt:
-                assert len(seq_ids) == 1
-                subquery_len = prompt_lens[i]
-                if sampling_params.prompt_logprobs is not None:
-                    # NOTE: prompt token positions do not need sample, skip
-                    categorized_sample_indices_start_idx += subquery_len - 1
-
-                categorized_sample_indices[
-                    sampling_params.sampling_type].append(
-                        (categorized_sample_indices_start_idx,
-                         categorized_sampled_token_indices_start_idx))
-                categorized_sample_indices_start_idx += 1
-                categorized_sampled_token_indices_start_idx += 1
-
-                if sampling_params.prompt_logprobs is not None:
-                    selected_token_indices.extend(
-                        range(selected_token_start_idx,
-                              selected_token_start_idx + subquery_len - 1))
-                selected_token_indices.append(selected_token_start_idx +
-                                              subquery_len - 1)
-                selected_token_start_idx += subquery_len
-
-                if sampling_params.seed is not None:
-                    seq_group_metadata.state.generator = torch.Generator(
-                        device=self.device).manual_seed(sampling_params.seed)
-            else:
-                num_seqs = len(seq_ids)
-                selected_token_indices.extend(
-                    range(selected_token_start_idx,
-                          selected_token_start_idx + num_seqs))
-                selected_token_start_idx += num_seqs
-
-                categorized_sample_indices[
-                    sampling_params.sampling_type].extend(
-                        zip(
-                            range(
-                                categorized_sample_indices_start_idx,
-                                categorized_sample_indices_start_idx +
-                                num_seqs),
-                            range(
-                                categorized_sampled_token_indices_start_idx,
-                                categorized_sampled_token_indices_start_idx +
-                                num_seqs)))
-                categorized_sample_indices_start_idx += num_seqs
-                categorized_sampled_token_indices_start_idx += num_seqs
-
-            if sampling_params.seed is not None:
-                generators.append(seq_group_metadata.state.generator)
-
-        selected_token_indices = torch.tensor(selected_token_indices,
-                                              dtype=torch.long)
-
-        categorized_sample_indices = {
-            t: maybe_expand_dim(torch.tensor(seq_ids, dtype=torch.int), 2, 2)
-            for t, seq_ids in categorized_sample_indices.items()
-        }
-
-        seq_data: Dict[int, SequenceData] = {}
-        for seq_group_metadata in seq_group_metadata_list:
-            seq_data.update(seq_group_metadata.seq_data)
-
-        sampling_metadata = SamplingMetadata(
-            seq_groups=seq_groups,
-            seq_data=seq_data,
-            prompt_lens=prompt_lens,
-            selected_token_indices=selected_token_indices,
-            categorized_sample_indices=categorized_sample_indices,
-            generators=generators,
-        )
-        return sampling_metadata
-
     def prepare_input_tensors(
         self,
         seq_group_metadata_list: List[SequenceGroupMetadata],
@@ -364,8 +272,15 @@ class CPUModelRunner:
                 (input_tokens, input_positions,
                  attn_metadata) = self._prepare_decode(seq_group_metadata_list)
                 prompt_lens = []
-            sampling_metadata = self._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens)
+            sampling_metadata = SamplingMetadata.prepare(
+                seq_group_metadata_list,
+                prompt_lens,
+                # subquery_lens is not needed if chunked prefill is not
+                # supported. Since CPU worker doesn't support chunked prefill
+                # just use prompt_lens instead.
+                prompt_lens,
+                self.device,
+                pin_memory=False)
             # Broadcast the metadata.
             metadata_dict = {
                 "input_tokens": input_tokens,
@@ -389,7 +304,6 @@ class CPUModelRunner:
                 selected_token_indices=selected_token_indices,
                 categorized_sample_indices=None,
                 generators=None,
-                perform_sampling=False,
             )
 
         return (input_tokens, input_positions, attn_metadata,
@@ -421,7 +335,7 @@ class CPUModelRunner:
         logits = self.model.compute_logits(hidden_states, sampling_metadata)
 
         # Only perform sampling in the driver worker.
-        if not sampling_metadata.perform_sampling:
+        if not self.is_driver_worker:
             return None
 
         # Sample the next token.

vllm/worker/model_runner.py

@@ -20,12 +20,11 @@ from vllm.lora.request import LoRARequest
 from vllm.lora.worker_manager import LRUCacheWorkerLoRAManager
 from vllm.model_executor import SamplingMetadata
 from vllm.model_executor.model_loader import get_model
-from vllm.sampling_params import SamplingParams, SamplingType
+from vllm.sampling_params import SamplingParams
 from vllm.sequence import (MultiModalData, SamplerOutput, SequenceData,
                            SequenceGroupMetadata)
-from vllm.utils import (CudaMemoryProfiler, async_tensor_h2d, is_hip,
-                        is_pin_memory_available, make_tensor_with_pad,
-                        maybe_expand_dim)
+from vllm.utils import (CudaMemoryProfiler, is_hip, is_pin_memory_available,
+                        make_tensor_with_pad)
 
 logger = init_logger(__name__)
 
@@ -547,108 +546,6 @@ class ModelRunner:
             slot_mapping=slot_mapping,
         )
 
-    def _prepare_sample(
-        self,
-        seq_group_metadata_list: List[SequenceGroupMetadata],
-        prompt_lens: List[int],
-        subquery_lens: Optional[List[int]],
-    ) -> SamplingMetadata:
-        seq_groups: List[Tuple[List[int], SamplingParams]] = []
-        selected_token_indices: List[int] = []
-        generators: List[torch.Generator] = []
-        selected_token_start_idx = 0
-        categorized_sample_indices: Dict[SamplingType,
-                                         List[Tuple[int, int]]] = {
-                                             t: []
-                                             for t in SamplingType
-                                         }
-        categorized_sample_indices_start_idx = 0
-        categorized_sampled_token_indices_start_idx = 0
-
-        for i, seq_group_metadata in enumerate(seq_group_metadata_list):
-            seq_ids = list(seq_group_metadata.seq_data.keys())
-            sampling_params = seq_group_metadata.sampling_params
-            seq_groups.append((seq_ids, sampling_params))
-
-            if seq_group_metadata.is_prompt:
-                assert len(seq_ids) == 1
-                assert subquery_lens is not None
-                subquery_len = subquery_lens[i]
-                if sampling_params.prompt_logprobs is not None:
-                    # NOTE: prompt token positions do not need sample, skip
-                    categorized_sample_indices_start_idx += subquery_len - 1
-
-                categorized_sample_indices[
-                    sampling_params.sampling_type].append(
-                        (categorized_sample_indices_start_idx,
-                         categorized_sampled_token_indices_start_idx))
-                categorized_sample_indices_start_idx += 1
-                categorized_sampled_token_indices_start_idx += 1
-
-                if sampling_params.prompt_logprobs is not None:
-                    selected_token_indices.extend(
-                        range(selected_token_start_idx,
-                              selected_token_start_idx + subquery_len - 1))
-                selected_token_indices.append(selected_token_start_idx +
-                                              subquery_len - 1)
-                selected_token_start_idx += subquery_len
-
-                if sampling_params.seed is not None:
-                    seq_group_metadata.state.generator = torch.Generator(
-                        device=self.device).manual_seed(sampling_params.seed)
-            else:
-                num_seqs = len(seq_ids)
-                selected_token_indices.extend(
-                    range(selected_token_start_idx,
-                          selected_token_start_idx + num_seqs))
-                selected_token_start_idx += num_seqs
-
-                categorized_sample_indices[
-                    sampling_params.sampling_type].extend(
-                        list(
-                            zip(
-                                range(
-                                    categorized_sample_indices_start_idx,
-                                    categorized_sample_indices_start_idx +
-                                    num_seqs),
-                                range(
-                                    categorized_sampled_token_indices_start_idx,
-                                    categorized_sampled_token_indices_start_idx
-                                    + num_seqs))))
-                categorized_sample_indices_start_idx += num_seqs
-                categorized_sampled_token_indices_start_idx += num_seqs
-
-            if sampling_params.seed is not None:
-                generators.append(seq_group_metadata.state.generator)
-
-        selected_token_indices = async_tensor_h2d(selected_token_indices,
-                                                  dtype=torch.long,
-                                                  target_device=self.device,
-                                                  pin_memory=self.pin_memory)
-
-        categorized_sample_indices = {
-            t: maybe_expand_dim(
-                async_tensor_h2d(seq_ids,
-                                 dtype=torch.int,
-                                 target_device=self.device,
-                                 pin_memory=self.pin_memory), 2, 2)
-            for t, seq_ids in categorized_sample_indices.items()
-        }
-
-        seq_data: Dict[int, SequenceData] = {}
-        for seq_group_metadata in seq_group_metadata_list:
-            seq_data.update(seq_group_metadata.seq_data)
-
-        sampling_metadata = SamplingMetadata(
-            seq_groups=seq_groups,
-            seq_data=seq_data,
-            prompt_lens=prompt_lens,
-            selected_token_indices=selected_token_indices,
-            categorized_sample_indices=categorized_sample_indices,
-            generators=generators,
-        )
-        return sampling_metadata
-
     def prepare_input_tensors(
         self,
         seq_group_metadata_list: List[SequenceGroupMetadata],
@@ -685,9 +582,9 @@ class ModelRunner:
                 decode_lora_requests,
                 decode_slot_mapping,
             ) = self._prepare_decode(decode_reqs)
-            sampling_metadata = self._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens)
+            sampling_metadata = SamplingMetadata.prepare(
+                seq_group_metadata_list, prompt_lens, subquery_lens,
+                self.device, self.pin_memory)
 
             if not self.scheduler_config.chunked_prefill_enabled:
                 assert (len(prefill_reqs) and len(decode_reqs)) == 0
@@ -788,12 +685,9 @@ class ModelRunner:
                     **metadata_dict)
             sampling_metadata = SamplingMetadata(
                 seq_groups=None,
-                seq_data=None,
-                prompt_lens=None,
                 selected_token_indices=selected_token_indices,
                 categorized_sample_indices=None,
-                generators=None,
-                perform_sampling=False,
+                num_prompts=0,
             )
 
             # if it is a mixed batch, decode attn_metadata is broadcasted
@@ -852,7 +746,7 @@ class ModelRunner:
         logits = self.model.compute_logits(hidden_states, sampling_metadata)
 
         # Only perform sampling in the driver worker.
-        if not sampling_metadata.perform_sampling:
+        if not self.is_driver_worker:
             return None
 
         # Sample the next token.
@@ -860,6 +754,7 @@ class ModelRunner:
             logits=logits,
             sampling_metadata=sampling_metadata,
         )
+
         return output
 
     @torch.inference_mode()

vllm/worker/neuron_model_runner.py

@@ -1,4 +1,4 @@
-from typing import Dict, List, Optional, Tuple
+from typing import List, Optional, Tuple
 
 import torch
 from torch import nn
@@ -8,10 +8,8 @@ from vllm.config import (DeviceConfig, ModelConfig, ParallelConfig,
 from vllm.logger import init_logger
 from vllm.model_executor import SamplingMetadata
 from vllm.model_executor.model_loader.neuron import get_neuron_model
-from vllm.sampling_params import SamplingParams, SamplingType
-from vllm.sequence import SamplerOutput, SequenceData, SequenceGroupMetadata
-from vllm.utils import (async_tensor_h2d, is_pin_memory_available,
-                        make_tensor_with_pad, maybe_expand_dim)
+from vllm.sequence import SamplerOutput, SequenceGroupMetadata
+from vllm.utils import is_pin_memory_available, make_tensor_with_pad
 
 logger = init_logger(__name__)
 
@@ -141,106 +139,6 @@ class NeuronModelRunner:
 
         return input_tokens, input_positions, input_block_ids
 
-    def _prepare_sample(
-        self,
-        seq_group_metadata_list: List[SequenceGroupMetadata],
-        prompt_lens: List[int],
-    ) -> SamplingMetadata:
-        seq_groups: List[Tuple[List[int], SamplingParams]] = []
-        selected_token_indices: List[int] = []
-        generators: List[torch.Generator] = []
-        selected_token_start_idx = 0
-        categorized_sample_indices: Dict[SamplingType,
-                                         List[Tuple[int, int]]] = {
-                                             t: []
-                                             for t in SamplingType
-                                         }
-        categorized_sample_indices_start_idx = 0
-        categorized_sampled_token_indices_start_idx = 0
-
-        for i, seq_group_metadata in enumerate(seq_group_metadata_list):
-            seq_ids = list(seq_group_metadata.seq_data.keys())
-            sampling_params = seq_group_metadata.sampling_params
-            seq_groups.append((seq_ids, sampling_params))
-
-            if seq_group_metadata.is_prompt:
-                assert len(seq_ids) == 1
-                assert prompt_lens is not None
-                prompt_len = prompt_lens[i]
-                if sampling_params.prompt_logprobs is not None:
-                    # NOTE: prompt token positions do not need sample, skip
-                    categorized_sample_indices_start_idx += prompt_len - 1
-
-                categorized_sample_indices[
-                    sampling_params.sampling_type].append(
-                        (categorized_sample_indices_start_idx,
-                         categorized_sampled_token_indices_start_idx))
-                categorized_sample_indices_start_idx += 1
-                categorized_sampled_token_indices_start_idx += 1
-
-                if sampling_params.prompt_logprobs is not None:
-                    selected_token_indices.extend(
-                        range(selected_token_start_idx,
-                              selected_token_start_idx + prompt_len - 1))
-                selected_token_indices.append(selected_token_start_idx +
-                                              prompt_len - 1)
-                selected_token_start_idx += prompt_len
-
-                if sampling_params.seed is not None:
-                    seq_group_metadata.state.generator = torch.Generator(
-                        device=self.device).manual_seed(sampling_params.seed)
-            else:
-                num_seqs = len(seq_ids)
-                selected_token_indices.extend(
-                    range(selected_token_start_idx,
-                          selected_token_start_idx + num_seqs))
-                selected_token_start_idx += num_seqs
-
-                categorized_sample_indices[
-                    sampling_params.sampling_type].extend(
-                        zip(
-                            range(
-                                categorized_sample_indices_start_idx,
-                                categorized_sample_indices_start_idx +
-                                num_seqs),
-                            range(
-                                categorized_sampled_token_indices_start_idx,
-                                categorized_sampled_token_indices_start_idx +
-                                num_seqs)))
-                categorized_sample_indices_start_idx += num_seqs
-                categorized_sampled_token_indices_start_idx += num_seqs
-
-            if sampling_params.seed is not None:
-                generators.append(seq_group_metadata.state.generator)
-
-        selected_token_indices = async_tensor_h2d(selected_token_indices,
-                                                  dtype=torch.long,
-                                                  target_device=self.device,
-                                                  pin_memory=self.pin_memory)
-
-        categorized_sample_indices = {
-            t: maybe_expand_dim(
-                async_tensor_h2d(seq_ids,
-                                 dtype=torch.int,
-                                 target_device=self.device,
-                                 pin_memory=self.pin_memory), 2, 2)
-            for t, seq_ids in categorized_sample_indices.items()
-        }
-
-        seq_data: Dict[int, SequenceData] = {}
-        for seq_group_metadata in seq_group_metadata_list:
-            seq_data.update(seq_group_metadata.seq_data)
-
-        sampling_metadata = SamplingMetadata(
-            seq_groups=seq_groups,
-            seq_data=seq_data,
-            prompt_lens=prompt_lens,
-            selected_token_indices=selected_token_indices,
-            categorized_sample_indices=categorized_sample_indices,
-            generators=generators,
-        )
-        return sampling_metadata
-
     def prepare_input_tensors(
         self,
         seq_group_metadata_list: List[SequenceGroupMetadata],
@@ -256,8 +154,15 @@ class NeuronModelRunner:
             (input_tokens, input_positions,
              input_block_ids) = self._prepare_decode(seq_group_metadata_list)
             prompt_lens = []
-        sampling_metadata = self._prepare_sample(seq_group_metadata_list,
-                                                 prompt_lens)
+        sampling_metadata = SamplingMetadata.prepare(
+            seq_group_metadata_list,
+            prompt_lens,
+            # subquery_lens is not needed if chunked prefill is not
+            # supported. Since neuron worker doesn't support chunked prefill
+            # just use prompt_lens instead.
+            prompt_lens,
+            self.device,
+            self.pin_memory)
 
         return (input_tokens, input_positions, input_block_ids,
                 sampling_metadata)