Fix result error when calling AllReduce serially.

mindspore/ccsrc/device/gpu/gpu_stream_assign.cc

@@ -40,6 +40,9 @@ void AssignGpuStream(const std::shared_ptr<session::KernelGraph> &kernel_graph)
     }
   }
   if (allreduce_kernels.size() > 1) {
+    // Assign multiple streams only when there's Recv node for AllReduce.
+    std::vector<SendRecvPair> send_recv_pairs;
+    if (FindAllReduceStreamSwitchPos(kernel_graph, &send_recv_pairs)) {
       DeviceStream comm_stream = nullptr;
       GPUDeviceManager::GetInstance().CreateStream(&comm_stream);
       std::transform(
@@ -47,14 +50,14 @@ void AssignGpuStream(const std::shared_ptr<session::KernelGraph> &kernel_graph)
           AnfAlgo::SetNodeAttr("stream_id", MakeValue(reinterpret_cast<uintptr_t>(comm_stream)), allreduce_kernel);
           return allreduce_kernel;
         });
-
-    std::vector<SendRecvPair> send_recv_pairs;
-    FindAllReduceStreamSwitchPos(kernel_graph, &send_recv_pairs);
       InsertStreamSwitchNode(kernel_graph, send_recv_pairs);
+    } else {
+      return;
+    }
   }
 }
 
-void FindAllReduceStreamSwitchPos(const std::shared_ptr<session::KernelGraph> &kernel_graph,
+bool FindAllReduceStreamSwitchPos(const std::shared_ptr<session::KernelGraph> &kernel_graph,
                                   std::vector<SendRecvPair> *send_recv_pairs) {
   auto execution_kernels = kernel_graph->execution_order();
   std::vector<CNodePtr>::iterator iter, iter_begin;
@@ -77,14 +80,15 @@ void FindAllReduceStreamSwitchPos(const std::shared_ptr<session::KernelGraph> &k
       std::vector<CNodePtr>::iterator mock_recv_node_iter =
         FindRecvNodePos(iter, iter_end, *iter, kAllReduceStreamSwitch);
       if (mock_recv_node_iter == iter_end) {
-        MS_LOG(WARNING) << "Can't find send node place before AllReduce node.";
+        MS_LOG(WARNING) << "Can't find recv node place after AllReduce node.";
-        continue;
+        return false;
       }
       SendRecvPair pair2 = {kAllReduceStreamSwitch, *iter, *mock_recv_node_iter, IntToSize(iter - iter_begin + 1),
                             IntToSize(mock_recv_node_iter - iter_begin)};
       send_recv_pairs->push_back(pair2);
     }
   }
+  return true;
 }
 
 std::vector<CNodePtr>::iterator FindSendNodePos(std::vector<CNodePtr>::iterator begin,

mindspore/ccsrc/device/gpu/gpu_stream_assign.h

@@ -48,7 +48,7 @@ struct StreamSwitchNode {
   }
 };
 void AssignGpuStream(const std::shared_ptr<session::KernelGraph> &kernel_graph);
-void FindAllReduceStreamSwitchPos(const std::shared_ptr<session::KernelGraph> &kernel_graph,
+bool FindAllReduceStreamSwitchPos(const std::shared_ptr<session::KernelGraph> &kernel_graph,
                                   std::vector<SendRecvPair> *send_recv_pairs);
 // Find Send node position according to "mock" recv node.
 // "mock" recv node is a gpu kernel node after a real Recv node, e.g. AllReduce node.

tests/st/nccl/test_nccl_all_reduce_op.py

@@ -75,3 +75,49 @@ def test_AllReduce():
     error2 = np.ones(shape=expect2.shape) * 1.0e-5
     assert np.all(diff2 < error2)
     assert output[2].shape() == expect2.shape
+
+
+class Net2(nn.Cell):
+    def __init__(self):
+        super(Net2, self).__init__()
+        self.x1 = Parameter(initializer(Tensor(x), x.shape), name='x1')
+
+        self.op0 = "sum"
+        self.op1 = "sum"
+        self.op2 = "sum"
+
+        self.all_reduce1 = P.AllReduce(self.op0, group=NCCL_WORLD_COMM_GROUP)
+        self.all_reduce2 = P.AllReduce(self.op1, group=NCCL_WORLD_COMM_GROUP)
+        self.all_reduce3 = P.AllReduce(self.op2, group=NCCL_WORLD_COMM_GROUP)
+
+    def construct(self):
+        x = self.all_reduce1(self.x1)
+        y = self.all_reduce2(x)
+        z = self.all_reduce3(y)
+        return (x, y, z)
+
+
+def test_AllReduce2():
+    all_reduce = Net2()
+    output = all_reduce()
+
+    expect0 = np.ones([3, 1, 3, 3]).astype(np.float32) * 0
+    for i in range(size):
+        part = np.ones([3, 1, 3, 3]).astype(np.float32) * 0.01 * (i + 1)
+        expect0 += part
+    diff0 = abs(output[0].asnumpy() - expect0)
+    error0 = np.ones(shape=expect0.shape) * 1.0e-5
+    assert np.all(diff0 < error0)
+    assert output[0].shape() == expect0.shape
+
+    expect1 = expect0 * size
+    diff1 = abs(output[1].asnumpy() - expect1)
+    error1 = np.ones(shape=expect1.shape) * 1.0e-5
+    assert np.all(diff1 < error1)
+    assert output[1].shape() == expect1.shape
+
+    expect2 = expect1 * size
+    diff2 = abs(output[2].asnumpy() - expect2)
+    error2 = np.ones(shape=expect2.shape) * 1.0e-5
+    assert np.all(diff2 < error2)
+    assert output[2].shape() == expect2.shape