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llvm-project/llvm/tools/llvm-xray/xray-stacks.cc

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//===- xray-stacks.cc - XRay Function Call Stack Accounting ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements stack-based accounting. It takes XRay traces, and
// collates statistics across these traces to show a breakdown of time spent
// at various points of the stack to provide insight into which functions
// spend the most time in terms of a call stack. We provide a few
// sorting/filtering options for zero'ing in on the useful stacks.
//
//===----------------------------------------------------------------------===//
#include <forward_list>
#include <numeric>
#include "func-id-helper.h"
#include "xray-registry.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FormatAdapters.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/XRay/Graph.h"
#include "llvm/XRay/InstrumentationMap.h"
#include "llvm/XRay/Trace.h"
using namespace llvm;
using namespace llvm::xray;
static cl::SubCommand Stack("stack", "Call stack accounting");
static cl::list<std::string> StackInputs(cl::Positional,
cl::desc("<xray trace>"), cl::Required,
cl::sub(Stack), cl::OneOrMore);
static cl::opt<bool>
StackKeepGoing("keep-going", cl::desc("Keep going on errors encountered"),
cl::sub(Stack), cl::init(false));
static cl::alias StackKeepGoing2("k", cl::aliasopt(StackKeepGoing),
cl::desc("Alias for -keep-going"),
cl::sub(Stack));
// TODO: Does there need to be an option to deduce tail or sibling calls?
static cl::opt<std::string> StacksInstrMap(
"instr_map",
cl::desc("instrumentation map used to identify function ids. "
"Currently supports elf file instrumentation maps."),
cl::sub(Stack), cl::init(""));
static cl::alias StacksInstrMap2("m", cl::aliasopt(StacksInstrMap),
cl::desc("Alias for -instr_map"),
cl::sub(Stack));
static cl::opt<bool>
SeparateThreadStacks("per-thread-stacks",
cl::desc("Report top stacks within each thread id"),
cl::sub(Stack), cl::init(false));
static cl::opt<bool>
AggregateThreads("aggregate-threads",
cl::desc("Aggregate stack times across threads"),
cl::sub(Stack), cl::init(false));
/// A helper struct to work with formatv and XRayRecords. Makes it easier to use
/// instrumentation map names or addresses in formatted output.
struct format_xray_record : public FormatAdapter<XRayRecord> {
explicit format_xray_record(XRayRecord record,
const FuncIdConversionHelper &conv)
: FormatAdapter<XRayRecord>(std::move(record)), Converter(&conv) {}
void format(raw_ostream &Stream, StringRef Style) override {
Stream << formatv(
"{FuncId: \"{0}\", ThreadId: \"{1}\", RecordType: \"{2}\"}",
Converter->SymbolOrNumber(Item.FuncId), Item.TId,
DecodeRecordType(Item.RecordType));
}
private:
Twine DecodeRecordType(uint16_t recordType) {
switch (recordType) {
case 0:
return Twine("Fn Entry");
case 1:
return Twine("Fn Exit");
default:
// TODO: Add Tail exit when it is added to llvm/XRay/XRayRecord.h
return Twine("Unknown");
}
}
const FuncIdConversionHelper *Converter;
};
/// The stack command will take a set of XRay traces as arguments, and collects
/// information about the stacks of instrumented functions that appear in the
/// traces. We track the following pieces of information:
///
/// - Total time: amount of time/cycles accounted for in the traces.
/// - Stack count: number of times a specific stack appears in the
/// traces. Only instrumented functions show up in stacks.
/// - Cumulative stack time: amount of time spent in a stack accumulated
/// across the invocations in the traces.
/// - Cumulative local time: amount of time spent in each instrumented
/// function showing up in a specific stack, accumulated across the traces.
///
/// Example output for the kind of data we'd like to provide looks like the
/// following:
///
/// Total time: 3.33234 s
/// Stack ID: ...
/// Stack Count: 2093
/// # Function Local Time (%) Stack Time (%)
/// 0 main 2.34 ms 0.07% 3.33234 s 100%
/// 1 foo() 3.30000 s 99.02% 3.33 s 99.92%
/// 2 bar() 30 ms 0.90% 30 ms 0.90%
///
/// We can also show distributions of the function call durations with
/// statistics at each level of the stack. This works by doing the following
/// algorithm:
///
/// 1. When unwinding, record the duration of each unwound function associated
/// with the path up to which the unwinding stops. For example:
///
/// Step Duration (? means has start time)
///
/// push a <start time> a = ?
/// push b <start time> a = ?, a->b = ?
/// push c <start time> a = ?, a->b = ?, a->b->c = ?
/// pop c <end time> a = ?, a->b = ?, emit duration(a->b->c)
/// pop b <end time> a = ?, emit duration(a->b)
/// push c <start time> a = ?, a->c = ?
/// pop c <end time> a = ?, emit duration(a->c)
/// pop a <end time> emit duration(a)
///
/// 2. We then account for the various stacks we've collected, and for each of
/// them will have measurements that look like the following (continuing
/// with the above simple example):
///
/// c : [<id("a->b->c"), [durations]>, <id("a->c"), [durations]>]
/// b : [<id("a->b"), [durations]>]
/// a : [<id("a"), [durations]>]
///
/// This allows us to compute, for each stack id, and each function that
/// shows up in the stack, some important statistics like:
///
/// - median
/// - 99th percentile
/// - mean + stddev
/// - count
///
/// 3. For cases where we don't have durations for some of the higher levels
/// of the stack (perhaps instrumentation wasn't activated when the stack was
/// entered), we can mark them appropriately.
///
/// Computing this data also allows us to implement lookup by call stack nodes,
/// so that we can find functions that show up in multiple stack traces and
/// show the statistical properties of that function in various contexts. We
/// can compute information similar to the following:
///
/// Function: 'c'
/// Stacks: 2 / 2
/// Stack ID: ...
/// Stack Count: ...
/// # Function ...
/// 0 a ...
/// 1 b ...
/// 2 c ...
///
/// Stack ID: ...
/// Stack Count: ...
/// # Function ...
/// 0 a ...
/// 1 c ...
/// ----------------...
///
/// Function: 'b'
/// Stacks: 1 / 2
/// Stack ID: ...
/// Stack Count: ...
/// # Function ...
/// 0 a ...
/// 1 b ...
/// 2 c ...
///
///
/// To do this we require a Trie data structure that will allow us to represent
/// all the call stacks of instrumented functions in an easily traversible
/// manner when we do the aggregations and lookups. For instrumented call
/// sequences like the following:
///
/// a()
/// b()
/// c()
/// d()
/// c()
///
/// We will have a representation like so:
///
/// a -> b -> c
/// | |
/// | +--> d
/// |
/// +--> c
///
/// We maintain a sequence of durations on the leaves and in the internal nodes
/// as we go through and process every record from the XRay trace. We also
/// maintain an index of unique functions, and provide a means of iterating
/// through all the instrumented call stacks which we know about.
struct TrieNode {
int32_t FuncId;
TrieNode *Parent;
SmallVector<TrieNode *, 4> Callees;
// Separate durations depending on whether the node is the deepest node in the
// stack.
SmallVector<int64_t, 4> TerminalDurations;
SmallVector<int64_t, 4> IntermediateDurations;
};
/// Merges together two TrieNodes with like function ids, aggregating their
/// callee lists and durations. The caller must provide storage where new merged
/// nodes can be allocated in the form of a linked list.
TrieNode *mergeTrieNodes(const TrieNode &Left, const TrieNode &Right,
TrieNode *NewParent,
std::forward_list<TrieNode> &NodeStore) {
assert(Left.FuncId == Right.FuncId);
NodeStore.push_front(TrieNode{Left.FuncId, NewParent, {}, {}, {}});
auto I = NodeStore.begin();
auto *Node = &*I;
// Build a map of callees from the left side.
DenseMap<int32_t, TrieNode *> LeftCalleesByFuncId;
for (auto *Callee : Left.Callees) {
LeftCalleesByFuncId[Callee->FuncId] = Callee;
}
// Iterate through the right side, either merging with the map values or
// directly adding to the Callees vector. The iteration also removes any
// merged values from the left side map.
for (auto *Callee : Right.Callees) {
auto iter = LeftCalleesByFuncId.find(Callee->FuncId);
if (iter != LeftCalleesByFuncId.end()) {
Node->Callees.push_back(
mergeTrieNodes(*(iter->second), *Callee, Node, NodeStore));
LeftCalleesByFuncId.erase(iter);
} else {
Node->Callees.push_back(Callee);
}
}
// Add any callees that weren't found in the right side.
for (auto MapPairIter : LeftCalleesByFuncId) {
Node->Callees.push_back(MapPairIter.second);
}
// Aggregate the durations.
for (auto duration : Left.TerminalDurations) {
Node->TerminalDurations.push_back(duration);
}
for (auto duration : Right.TerminalDurations) {
Node->TerminalDurations.push_back(duration);
}
for (auto duration : Left.IntermediateDurations) {
Node->IntermediateDurations.push_back(duration);
}
for (auto duration : Right.IntermediateDurations) {
Node->IntermediateDurations.push_back(duration);
}
return Node;
}
class StackTrie {
// We maintain pointers to the roots of the tries we see.
DenseMap<uint32_t, SmallVector<TrieNode *, 4>> Roots;
// We make sure all the nodes are accounted for in this list.
std::forward_list<TrieNode> NodeStore;
// A map of thread ids to pairs call stack trie nodes and their start times.
DenseMap<uint32_t, SmallVector<std::pair<TrieNode *, uint64_t>, 8>>
ThreadStackMap;
TrieNode *createTrieNode(uint32_t ThreadId, int32_t FuncId,
TrieNode *Parent) {
NodeStore.push_front(TrieNode{FuncId, Parent, {}, {}, {}});
auto I = NodeStore.begin();
auto *Node = &*I;
if (!Parent)
Roots[ThreadId].push_back(Node);
return Node;
}
TrieNode *findRootNode(uint32_t ThreadId, int32_t FuncId) {
const auto &RootsByThread = Roots[ThreadId];
auto I = find_if(RootsByThread,
[&](TrieNode *N) { return N->FuncId == FuncId; });
return (I == RootsByThread.end()) ? nullptr : *I;
}
public:
enum class AccountRecordStatus {
OK, // Successfully processed
ENTRY_NOT_FOUND, // An exit record had no matching call stack entry
UNKNOWN_RECORD_TYPE
};
struct AccountRecordState {
// We keep track of whether the call stack is currently unwinding.
bool wasLastRecordExit;
static AccountRecordState CreateInitialState() { return {false}; }
};
AccountRecordStatus accountRecord(const XRayRecord &R,
AccountRecordState *state) {
auto &TS = ThreadStackMap[R.TId];
switch (R.Type) {
case RecordTypes::ENTER: {
state->wasLastRecordExit = false;
// When we encounter a new function entry, we want to record the TSC for
// that entry, and the function id. Before doing so we check the top of
// the stack to see if there are callees that already represent this
// function.
if (TS.empty()) {
auto *Root = findRootNode(R.TId, R.FuncId);
TS.emplace_back(Root ? Root : createTrieNode(R.TId, R.FuncId, nullptr),
R.TSC);
return AccountRecordStatus::OK;
}
auto &Top = TS.back();
auto I = find_if(Top.first->Callees,
[&](TrieNode *N) { return N->FuncId == R.FuncId; });
if (I == Top.first->Callees.end()) {
// We didn't find the callee in the stack trie, so we're going to
// add to the stack then set up the pointers properly.
auto N = createTrieNode(R.TId, R.FuncId, Top.first);
Top.first->Callees.emplace_back(N);
// Top may be invalidated after this statement.
TS.emplace_back(N, R.TSC);
} else {
// We found the callee in the stack trie, so we'll use that pointer
// instead, add it to the stack associated with the TSC.
TS.emplace_back(*I, R.TSC);
}
return AccountRecordStatus::OK;
}
case RecordTypes::EXIT: {
bool wasLastRecordExit = state->wasLastRecordExit;
state->wasLastRecordExit = true;
// The exit case is more interesting, since we want to be able to deduce
// missing exit records. To do that properly, we need to look up the stack
// and see whether the exit record matches any of the entry records. If it
// does match, we attempt to record the durations as we pop the stack to
// where we see the parent.
if (TS.empty()) {
// Short circuit, and say we can't find it.
return AccountRecordStatus::ENTRY_NOT_FOUND;
}
auto FunctionEntryMatch =
find_if(reverse(TS), [&](const std::pair<TrieNode *, uint64_t> &E) {
return E.first->FuncId == R.FuncId;
});
auto status = AccountRecordStatus::OK;
if (FunctionEntryMatch == TS.rend()) {
status = AccountRecordStatus::ENTRY_NOT_FOUND;
} else {
// Account for offset of 1 between reverse and forward iterators. We
// want the forward iterator to include the function that is exited.
++FunctionEntryMatch;
}
auto I = FunctionEntryMatch.base();
for (auto &E : make_range(I, TS.end() - 1))
E.first->IntermediateDurations.push_back(std::max(E.second, R.TSC) -
std::min(E.second, R.TSC));
auto &Deepest = TS.back();
if (wasLastRecordExit)
Deepest.first->IntermediateDurations.push_back(
std::max(Deepest.second, R.TSC) - std::min(Deepest.second, R.TSC));
else
Deepest.first->TerminalDurations.push_back(
std::max(Deepest.second, R.TSC) - std::min(Deepest.second, R.TSC));
TS.erase(I, TS.end());
return status;
}
}
return AccountRecordStatus::UNKNOWN_RECORD_TYPE;
}
bool isEmpty() const { return Roots.empty(); }
void printStack(raw_ostream &OS, const TrieNode *Top,
FuncIdConversionHelper &FN) {
// Traverse the pointers up to the parent, noting the sums, then print
// in reverse order (callers at top, callees down bottom).
SmallVector<const TrieNode *, 8> CurrentStack;
for (auto *F = Top; F != nullptr; F = F->Parent)
CurrentStack.push_back(F);
int Level = 0;
OS << formatv("{0,-5} {1,-60} {2,+12} {3,+16}\n", "lvl", "function",
"count", "sum");
for (auto *F :
reverse(make_range(CurrentStack.begin() + 1, CurrentStack.end()))) {
auto Sum = std::accumulate(F->IntermediateDurations.begin(),
F->IntermediateDurations.end(), 0LL);
auto FuncId = FN.SymbolOrNumber(F->FuncId);
OS << formatv("#{0,-4} {1,-60} {2,+12} {3,+16}\n", Level++,
FuncId.size() > 60 ? FuncId.substr(0, 57) + "..." : FuncId,
F->IntermediateDurations.size(), Sum);
}
auto *Leaf = *CurrentStack.begin();
auto LeafSum = std::accumulate(Leaf->TerminalDurations.begin(),
Leaf->TerminalDurations.end(), 0LL);
auto LeafFuncId = FN.SymbolOrNumber(Leaf->FuncId);
OS << formatv("#{0,-4} {1,-60} {2,+12} {3,+16}\n", Level++,
LeafFuncId.size() > 60 ? LeafFuncId.substr(0, 57) + "..."
: LeafFuncId,
Leaf->TerminalDurations.size(), LeafSum);
OS << "\n";
}
/// Prints top stacks for each thread.
void printPerThread(raw_ostream &OS, FuncIdConversionHelper &FN) {
for (auto iter : Roots) {
OS << "Thread " << iter.first << ":\n";
print(OS, FN, iter.second);
OS << "\n";
}
}
/// Prints top stacks from looking at all the leaves and ignoring thread IDs.
/// Stacks that consist of the same function IDs but were called in different
/// thread IDs are not considered unique in this printout.
void printIgnoringThreads(raw_ostream &OS, FuncIdConversionHelper &FN) {
SmallVector<TrieNode *, 4> RootValues;
// Function to pull the values out of a map iterator.
using RootsType = decltype(Roots.begin())::value_type;
auto MapValueFn = [](const RootsType &Value) { return Value.second; };
for (const auto &RootNodeRange :
make_range(map_iterator(Roots.begin(), MapValueFn),
map_iterator(Roots.end(), MapValueFn))) {
for (auto *RootNode : RootNodeRange)
RootValues.push_back(RootNode);
}
print(OS, FN, RootValues);
}
/// Merges the trie by thread id before printing top stacks.
void printAggregatingThreads(raw_ostream &OS, FuncIdConversionHelper &FN) {
std::forward_list<TrieNode> AggregatedNodeStore;
SmallVector<TrieNode *, 4> RootValues;
for (auto MapIter : Roots) {
const auto &RootNodeVector = MapIter.second;
for (auto *Node : RootNodeVector) {
auto MaybeFoundIter = find_if(RootValues, [Node](TrieNode *elem) {
return Node->FuncId == elem->FuncId;
});
if (MaybeFoundIter == RootValues.end()) {
RootValues.push_back(Node);
} else {
RootValues.push_back(mergeTrieNodes(**MaybeFoundIter, *Node, nullptr,
AggregatedNodeStore));
RootValues.erase(MaybeFoundIter);
}
}
}
print(OS, FN, RootValues);
}
void print(raw_ostream &OS, FuncIdConversionHelper &FN,
SmallVector<TrieNode *, 4> RootValues) {
// Go through each of the roots, and traverse the call stack, producing the
// aggregates as you go along. Remember these aggregates and stacks, and
// show summary statistics about:
//
// - Total number of unique stacks
// - Top 10 stacks by count
// - Top 10 stacks by aggregate duration
SmallVector<std::pair<const TrieNode *, uint64_t>, 11> TopStacksByCount;
SmallVector<std::pair<const TrieNode *, uint64_t>, 11> TopStacksBySum;
auto greater_second = [](const std::pair<const TrieNode *, uint64_t> &A,
const std::pair<const TrieNode *, uint64_t> &B) {
return A.second > B.second;
};
uint64_t UniqueStacks = 0;
for (const auto *N : RootValues) {
SmallVector<const TrieNode *, 16> S;
S.emplace_back(N);
while (!S.empty()) {
auto Top = S.pop_back_val();
// We only start printing the stack (by walking up the parent pointers)
// when we get to a leaf function.
if (!Top->TerminalDurations.empty()) {
++UniqueStacks;
auto TopSum = std::accumulate(Top->TerminalDurations.begin(),
Top->TerminalDurations.end(), 0uLL);
{
auto E = std::make_pair(Top, TopSum);
TopStacksBySum.insert(std::lower_bound(TopStacksBySum.begin(),
TopStacksBySum.end(), E,
greater_second),
E);
if (TopStacksBySum.size() == 11)
TopStacksBySum.pop_back();
}
{
auto E = std::make_pair(Top, Top->TerminalDurations.size());
TopStacksByCount.insert(std::lower_bound(TopStacksByCount.begin(),
TopStacksByCount.end(), E,
greater_second),
E);
if (TopStacksByCount.size() == 11)
TopStacksByCount.pop_back();
}
}
for (const auto *C : Top->Callees)
S.push_back(C);
}
}
// Now print the statistics in the end.
OS << "\n";
OS << "Unique Stacks: " << UniqueStacks << "\n";
OS << "Top 10 Stacks by leaf sum:\n\n";
for (const auto &P : TopStacksBySum) {
OS << "Sum: " << P.second << "\n";
printStack(OS, P.first, FN);
}
OS << "\n";
OS << "Top 10 Stacks by leaf count:\n\n";
for (const auto &P : TopStacksByCount) {
OS << "Count: " << P.second << "\n";
printStack(OS, P.first, FN);
}
OS << "\n";
}
};
std::string CreateErrorMessage(StackTrie::AccountRecordStatus Error,
const XRayRecord &Record,
const FuncIdConversionHelper &Converter) {
switch (Error) {
case StackTrie::AccountRecordStatus::ENTRY_NOT_FOUND:
return formatv("Found record {0} with no matching function entry\n",
format_xray_record(Record, Converter));
default:
return formatv("Unknown error type for record {0}\n",
format_xray_record(Record, Converter));
}
}
static CommandRegistration Unused(&Stack, []() -> Error {
// Load each file provided as a command-line argument. For each one of them
// account to a single StackTrie, and just print the whole trie for now.
StackTrie ST;
InstrumentationMap Map;
if (!StacksInstrMap.empty()) {
auto InstrumentationMapOrError = loadInstrumentationMap(StacksInstrMap);
if (!InstrumentationMapOrError)
return joinErrors(
make_error<StringError>(
Twine("Cannot open instrumentation map: ") + StacksInstrMap,
std::make_error_code(std::errc::invalid_argument)),
InstrumentationMapOrError.takeError());
Map = std::move(*InstrumentationMapOrError);
}
if (SeparateThreadStacks && AggregateThreads)
return make_error<StringError>(
Twine("Can't specify options for per thread reporting and reporting "
"that aggregates threads."),
std::make_error_code(std::errc::invalid_argument));
symbolize::LLVMSymbolizer::Options Opts(
symbolize::FunctionNameKind::LinkageName, true, true, false, "");
symbolize::LLVMSymbolizer Symbolizer(Opts);
FuncIdConversionHelper FuncIdHelper(StacksInstrMap, Symbolizer,
Map.getFunctionAddresses());
// TODO: Someday, support output to files instead of just directly to
// standard output.
for (const auto &Filename : StackInputs) {
auto TraceOrErr = loadTraceFile(Filename);
if (!TraceOrErr) {
if (!StackKeepGoing)
return joinErrors(
make_error<StringError>(
Twine("Failed loading input file '") + Filename + "'",
std::make_error_code(std::errc::invalid_argument)),
TraceOrErr.takeError());
logAllUnhandledErrors(TraceOrErr.takeError(), errs(), "");
continue;
}
auto &T = *TraceOrErr;
StackTrie::AccountRecordState AccountRecordState =
StackTrie::AccountRecordState::CreateInitialState();
for (const auto &Record : T) {
auto error = ST.accountRecord(Record, &AccountRecordState);
if (error != StackTrie::AccountRecordStatus::OK) {
if (!StackKeepGoing)
return make_error<StringError>(
CreateErrorMessage(error, Record, FuncIdHelper),
make_error_code(errc::illegal_byte_sequence));
errs() << CreateErrorMessage(error, Record, FuncIdHelper);
}
}
}
if (ST.isEmpty()) {
return make_error<StringError>(
"No instrumented calls were accounted in the input file.",
make_error_code(errc::result_out_of_range));
}
if (AggregateThreads) {
ST.printAggregatingThreads(outs(), FuncIdHelper);
} else if (SeparateThreadStacks) {
ST.printPerThread(outs(), FuncIdHelper);
} else {
ST.printIgnoringThreads(outs(), FuncIdHelper);
}
return Error::success();
});
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