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llvm-mirror/tools/llvm-exegesis/llvm-exegesis.cpp
Vy Nguyen 0724050861 Reland [llvm-exegesis] Add benchmark latency option on X86 that uses LBR for more precise measurements. 
Starting with Skylake, the LBR contains the precise number of cycles between the two
        consecutive branches.
        Making use of this will hopefully make the measurements more precise than the
        existing methods of using RDTSC.

                Differential Revision: https://reviews.llvm.org/D77422

New change: check for existence of field `cycles` in perf_branch_entry before enabling this mode.
This should prevent compilation errors when building for older kernel whose headers don't support it.
2020-07-27 12:38:05 -04:00

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//===-- llvm-exegesis.cpp ---------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Measures execution properties (latencies/uops) of an instruction.
///
//===----------------------------------------------------------------------===//
#include "lib/Analysis.h"
#include "lib/BenchmarkResult.h"
#include "lib/BenchmarkRunner.h"
#include "lib/Clustering.h"
#include "lib/Error.h"
#include "lib/LlvmState.h"
#include "lib/PerfHelper.h"
#include "lib/SnippetFile.h"
#include "lib/SnippetRepetitor.h"
#include "lib/Target.h"
#include "lib/TargetSelect.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCInstBuilder.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCParser/MCAsmParser.h"
#include "llvm/MC/MCParser/MCTargetAsmParser.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/TargetSelect.h"
#include <algorithm>
#include <string>
namespace llvm {
namespace exegesis {
static cl::OptionCategory Options("llvm-exegesis options");
static cl::OptionCategory BenchmarkOptions("llvm-exegesis benchmark options");
static cl::OptionCategory AnalysisOptions("llvm-exegesis analysis options");
static cl::opt<int> OpcodeIndex(
"opcode-index",
cl::desc("opcode to measure, by index, or -1 to measure all opcodes"),
cl::cat(BenchmarkOptions), cl::init(0));
static cl::opt<std::string>
OpcodeNames("opcode-name",
cl::desc("comma-separated list of opcodes to measure, by name"),
cl::cat(BenchmarkOptions), cl::init(""));
static cl::opt<std::string> SnippetsFile("snippets-file",
cl::desc("code snippets to measure"),
cl::cat(BenchmarkOptions),
cl::init(""));
static cl::opt<std::string>
BenchmarkFile("benchmarks-file",
cl::desc("File to read (analysis mode) or write "
"(latency/uops/inverse_throughput modes) benchmark "
"results. “-” uses stdin/stdout."),
cl::cat(Options), cl::init(""));
static cl::opt<exegesis::InstructionBenchmark::ModeE> BenchmarkMode(
"mode", cl::desc("the mode to run"), cl::cat(Options),
cl::values(clEnumValN(exegesis::InstructionBenchmark::Latency, "latency",
"Instruction Latency"),
clEnumValN(exegesis::InstructionBenchmark::InverseThroughput,
"inverse_throughput",
"Instruction Inverse Throughput"),
clEnumValN(exegesis::InstructionBenchmark::Uops, "uops",
"Uop Decomposition"),
// When not asking for a specific benchmark mode,
// we'll analyse the results.
clEnumValN(exegesis::InstructionBenchmark::Unknown, "analysis",
"Analysis")));
static cl::opt<exegesis::InstructionBenchmark::ResultAggregationModeE>
ResultAggMode(
"result-aggregation-mode",
cl::desc("How to aggregate multi-values result"), cl::cat(Options),
cl::values(clEnumValN(exegesis::InstructionBenchmark::Min, "min",
"Keep min reading"),
clEnumValN(exegesis::InstructionBenchmark::Max, "max",
"Keep max reading"),
clEnumValN(exegesis::InstructionBenchmark::Mean, "mean",
"Compute mean of all readings"),
clEnumValN(exegesis::InstructionBenchmark::MinVariance,
"min-variance",
"Keep readings set with min-variance")),
cl::init(exegesis::InstructionBenchmark::Min));
static cl::opt<exegesis::InstructionBenchmark::RepetitionModeE> RepetitionMode(
"repetition-mode", cl::desc("how to repeat the instruction snippet"),
cl::cat(BenchmarkOptions),
cl::values(
clEnumValN(exegesis::InstructionBenchmark::Duplicate, "duplicate",
"Duplicate the snippet"),
clEnumValN(exegesis::InstructionBenchmark::Loop, "loop",
"Loop over the snippet"),
clEnumValN(exegesis::InstructionBenchmark::AggregateMin, "min",
"All of the above and take the minimum of measurements")),
cl::init(exegesis::InstructionBenchmark::Duplicate));
static cl::opt<unsigned>
NumRepetitions("num-repetitions",
cl::desc("number of time to repeat the asm snippet"),
cl::cat(BenchmarkOptions), cl::init(10000));
static cl::opt<unsigned> MaxConfigsPerOpcode(
"max-configs-per-opcode",
cl::desc(
"allow to snippet generator to generate at most that many configs"),
cl::cat(BenchmarkOptions), cl::init(1));
static cl::opt<bool> IgnoreInvalidSchedClass(
"ignore-invalid-sched-class",
cl::desc("ignore instructions that do not define a sched class"),
cl::cat(BenchmarkOptions), cl::init(false));
static cl::opt<exegesis::InstructionBenchmarkClustering::ModeE>
AnalysisClusteringAlgorithm(
"analysis-clustering", cl::desc("the clustering algorithm to use"),
cl::cat(AnalysisOptions),
cl::values(clEnumValN(exegesis::InstructionBenchmarkClustering::Dbscan,
"dbscan", "use DBSCAN/OPTICS algorithm"),
clEnumValN(exegesis::InstructionBenchmarkClustering::Naive,
"naive", "one cluster per opcode")),
cl::init(exegesis::InstructionBenchmarkClustering::Dbscan));
static cl::opt<unsigned> AnalysisDbscanNumPoints(
"analysis-numpoints",
cl::desc("minimum number of points in an analysis cluster (dbscan only)"),
cl::cat(AnalysisOptions), cl::init(3));
static cl::opt<float> AnalysisClusteringEpsilon(
"analysis-clustering-epsilon",
cl::desc("epsilon for benchmark point clustering"),
cl::cat(AnalysisOptions), cl::init(0.1));
static cl::opt<float> AnalysisInconsistencyEpsilon(
"analysis-inconsistency-epsilon",
cl::desc("epsilon for detection of when the cluster is different from the "
"LLVM schedule profile values"),
cl::cat(AnalysisOptions), cl::init(0.1));
static cl::opt<std::string>
AnalysisClustersOutputFile("analysis-clusters-output-file", cl::desc(""),
cl::cat(AnalysisOptions), cl::init(""));
static cl::opt<std::string>
AnalysisInconsistenciesOutputFile("analysis-inconsistencies-output-file",
cl::desc(""), cl::cat(AnalysisOptions),
cl::init(""));
static cl::list<std::string>
AllowedHostCpus("allowed-host-cpu",
cl::desc("If specified, only run the benchmark if the host "
"CPU matches the names"),
cl::cat(Options), cl::ZeroOrMore);
static cl::opt<bool> AnalysisDisplayUnstableOpcodes(
"analysis-display-unstable-clusters",
cl::desc("if there is more than one benchmark for an opcode, said "
"benchmarks may end up not being clustered into the same cluster "
"if the measured performance characteristics are different. by "
"default all such opcodes are filtered out. this flag will "
"instead show only such unstable opcodes"),
cl::cat(AnalysisOptions), cl::init(false));
static cl::opt<std::string> CpuName(
"mcpu",
cl::desc("cpu name to use for pfm counters, leave empty to autodetect"),
cl::cat(Options), cl::init(""));
static cl::opt<bool>
DumpObjectToDisk("dump-object-to-disk",
cl::desc("dumps the generated benchmark object to disk "
"and prints a message to access it"),
cl::cat(BenchmarkOptions), cl::init(true));
static ExitOnError ExitOnErr("llvm-exegesis error: ");
// Helper function that logs the error(s) and exits.
template <typename... ArgTs> static void ExitWithError(ArgTs &&... Args) {
ExitOnErr(make_error<Failure>(std::forward<ArgTs>(Args)...));
}
// Check Err. If it's in a failure state log the file error(s) and exit.
static void ExitOnFileError(const Twine &FileName, Error Err) {
if (Err) {
ExitOnErr(createFileError(FileName, std::move(Err)));
}
}
// Check E. If it's in a success state then return the contained value.
// If it's in a failure state log the file error(s) and exit.
template <typename T>
T ExitOnFileError(const Twine &FileName, Expected<T> &&E) {
ExitOnFileError(FileName, E.takeError());
return std::move(*E);
}
// Checks that only one of OpcodeNames, OpcodeIndex or SnippetsFile is provided,
// and returns the opcode indices or {} if snippets should be read from
// `SnippetsFile`.
static std::vector<unsigned> getOpcodesOrDie(const MCInstrInfo &MCInstrInfo) {
const size_t NumSetFlags = (OpcodeNames.empty() ? 0 : 1) +
(OpcodeIndex == 0 ? 0 : 1) +
(SnippetsFile.empty() ? 0 : 1);
if (NumSetFlags != 1) {
ExitOnErr.setBanner("llvm-exegesis: ");
ExitWithError("please provide one and only one of 'opcode-index', "
"'opcode-name' or 'snippets-file'");
}
if (!SnippetsFile.empty())
return {};
if (OpcodeIndex > 0)
return {static_cast<unsigned>(OpcodeIndex)};
if (OpcodeIndex < 0) {
std::vector<unsigned> Result;
for (unsigned I = 1, E = MCInstrInfo.getNumOpcodes(); I < E; ++I)
Result.push_back(I);
return Result;
}
// Resolve opcode name -> opcode.
const auto ResolveName = [&MCInstrInfo](StringRef OpcodeName) -> unsigned {
for (unsigned I = 1, E = MCInstrInfo.getNumOpcodes(); I < E; ++I)
if (MCInstrInfo.getName(I) == OpcodeName)
return I;
return 0u;
};
SmallVector<StringRef, 2> Pieces;
StringRef(OpcodeNames.getValue())
.split(Pieces, ",", /* MaxSplit */ -1, /* KeepEmpty */ false);
std::vector<unsigned> Result;
for (const StringRef &OpcodeName : Pieces) {
if (unsigned Opcode = ResolveName(OpcodeName))
Result.push_back(Opcode);
else
ExitWithError(Twine("unknown opcode ").concat(OpcodeName));
}
return Result;
}
// Generates code snippets for opcode `Opcode`.
static Expected<std::vector<BenchmarkCode>>
generateSnippets(const LLVMState &State, unsigned Opcode,
const BitVector &ForbiddenRegs) {
const Instruction &Instr = State.getIC().getInstr(Opcode);
const MCInstrDesc &InstrDesc = Instr.Description;
// Ignore instructions that we cannot run.
if (InstrDesc.isPseudo())
return make_error<Failure>("Unsupported opcode: isPseudo");
if (InstrDesc.isBranch() || InstrDesc.isIndirectBranch())
return make_error<Failure>("Unsupported opcode: isBranch/isIndirectBranch");
if (InstrDesc.isCall() || InstrDesc.isReturn())
return make_error<Failure>("Unsupported opcode: isCall/isReturn");
const std::vector<InstructionTemplate> InstructionVariants =
State.getExegesisTarget().generateInstructionVariants(
Instr, MaxConfigsPerOpcode);
SnippetGenerator::Options SnippetOptions;
SnippetOptions.MaxConfigsPerOpcode = MaxConfigsPerOpcode;
const std::unique_ptr<SnippetGenerator> Generator =
State.getExegesisTarget().createSnippetGenerator(BenchmarkMode, State,
SnippetOptions);
if (!Generator)
ExitWithError("cannot create snippet generator");
std::vector<BenchmarkCode> Benchmarks;
for (const InstructionTemplate &Variant : InstructionVariants) {
if (Benchmarks.size() >= MaxConfigsPerOpcode)
break;
if (auto Err = Generator->generateConfigurations(Variant, Benchmarks,
ForbiddenRegs))
return std::move(Err);
}
return Benchmarks;
}
void benchmarkMain() {
#ifndef HAVE_LIBPFM
ExitWithError("benchmarking unavailable, LLVM was built without libpfm.");
#endif
if (exegesis::pfm::pfmInitialize())
ExitWithError("cannot initialize libpfm");
InitializeNativeTarget();
InitializeNativeTargetAsmPrinter();
InitializeNativeTargetAsmParser();
InitializeNativeExegesisTarget();
const LLVMState State(CpuName);
llvm::StringRef ActualCpu = State.getTargetMachine().getTargetCPU();
for (auto Begin = AllowedHostCpus.begin(); Begin != AllowedHostCpus.end();
++Begin) {
if (ActualCpu != *Begin)
ExitWithError(llvm::Twine("Unexpected host CPU ").concat(ActualCpu));
}
const std::unique_ptr<BenchmarkRunner> Runner =
ExitOnErr(State.getExegesisTarget().createBenchmarkRunner(
BenchmarkMode, State, ResultAggMode));
if (!Runner) {
ExitWithError("cannot create benchmark runner");
}
const auto Opcodes = getOpcodesOrDie(State.getInstrInfo());
SmallVector<std::unique_ptr<const SnippetRepetitor>, 2> Repetitors;
if (RepetitionMode != InstructionBenchmark::RepetitionModeE::AggregateMin)
Repetitors.emplace_back(SnippetRepetitor::Create(RepetitionMode, State));
else {
for (InstructionBenchmark::RepetitionModeE RepMode :
{InstructionBenchmark::RepetitionModeE::Duplicate,
InstructionBenchmark::RepetitionModeE::Loop})
Repetitors.emplace_back(SnippetRepetitor::Create(RepMode, State));
}
BitVector AllReservedRegs;
llvm::for_each(Repetitors,
[&AllReservedRegs](
const std::unique_ptr<const SnippetRepetitor> &Repetitor) {
AllReservedRegs |= Repetitor->getReservedRegs();
});
std::vector<BenchmarkCode> Configurations;
if (!Opcodes.empty()) {
for (const unsigned Opcode : Opcodes) {
// Ignore instructions without a sched class if
// -ignore-invalid-sched-class is passed.
if (IgnoreInvalidSchedClass &&
State.getInstrInfo().get(Opcode).getSchedClass() == 0) {
errs() << State.getInstrInfo().getName(Opcode)
<< ": ignoring instruction without sched class\n";
continue;
}
auto ConfigsForInstr = generateSnippets(State, Opcode, AllReservedRegs);
if (!ConfigsForInstr) {
logAllUnhandledErrors(
ConfigsForInstr.takeError(), errs(),
Twine(State.getInstrInfo().getName(Opcode)).concat(": "));
continue;
}
std::move(ConfigsForInstr->begin(), ConfigsForInstr->end(),
std::back_inserter(Configurations));
}
} else {
Configurations = ExitOnErr(readSnippets(State, SnippetsFile));
}
if (NumRepetitions == 0) {
ExitOnErr.setBanner("llvm-exegesis: ");
ExitWithError("--num-repetitions must be greater than zero");
}
// Write to standard output if file is not set.
if (BenchmarkFile.empty())
BenchmarkFile = "-";
for (const BenchmarkCode &Conf : Configurations) {
InstructionBenchmark Result = ExitOnErr(Runner->runConfiguration(
Conf, NumRepetitions, Repetitors, DumpObjectToDisk));
ExitOnFileError(BenchmarkFile, Result.writeYaml(State, BenchmarkFile));
}
exegesis::pfm::pfmTerminate();
}
// Prints the results of running analysis pass `Pass` to file `OutputFilename`
// if OutputFilename is non-empty.
template <typename Pass>
static void maybeRunAnalysis(const Analysis &Analyzer, const std::string &Name,
const std::string &OutputFilename) {
if (OutputFilename.empty())
return;
if (OutputFilename != "-") {
errs() << "Printing " << Name << " results to file '" << OutputFilename
<< "'\n";
}
std::error_code ErrorCode;
raw_fd_ostream ClustersOS(OutputFilename, ErrorCode,
sys::fs::FA_Read | sys::fs::FA_Write);
if (ErrorCode)
ExitOnFileError(OutputFilename, errorCodeToError(ErrorCode));
if (auto Err = Analyzer.run<Pass>(ClustersOS))
ExitOnFileError(OutputFilename, std::move(Err));
}
static void analysisMain() {
ExitOnErr.setBanner("llvm-exegesis: ");
if (BenchmarkFile.empty())
ExitWithError("--benchmarks-file must be set");
if (AnalysisClustersOutputFile.empty() &&
AnalysisInconsistenciesOutputFile.empty()) {
ExitWithError(
"for --mode=analysis: At least one of --analysis-clusters-output-file"
"and --analysis-inconsistencies-output-file must be specified");
}
InitializeNativeTarget();
InitializeNativeTargetAsmPrinter();
InitializeNativeTargetDisassembler();
// Read benchmarks.
const LLVMState State("");
const std::vector<InstructionBenchmark> Points = ExitOnFileError(
BenchmarkFile, InstructionBenchmark::readYamls(State, BenchmarkFile));
outs() << "Parsed " << Points.size() << " benchmark points\n";
if (Points.empty()) {
errs() << "no benchmarks to analyze\n";
return;
}
// FIXME: Check that all points have the same triple/cpu.
// FIXME: Merge points from several runs (latency and uops).
std::string Error;
const auto *TheTarget =
TargetRegistry::lookupTarget(Points[0].LLVMTriple, Error);
if (!TheTarget) {
errs() << "unknown target '" << Points[0].LLVMTriple << "'\n";
return;
}
std::unique_ptr<MCInstrInfo> InstrInfo(TheTarget->createMCInstrInfo());
const auto Clustering = ExitOnErr(InstructionBenchmarkClustering::create(
Points, AnalysisClusteringAlgorithm, AnalysisDbscanNumPoints,
AnalysisClusteringEpsilon, InstrInfo->getNumOpcodes()));
const Analysis Analyzer(*TheTarget, std::move(InstrInfo), Clustering,
AnalysisInconsistencyEpsilon,
AnalysisDisplayUnstableOpcodes);
maybeRunAnalysis<Analysis::PrintClusters>(Analyzer, "analysis clusters",
AnalysisClustersOutputFile);
maybeRunAnalysis<Analysis::PrintSchedClassInconsistencies>(
Analyzer, "sched class consistency analysis",
AnalysisInconsistenciesOutputFile);
}
} // namespace exegesis
} // namespace llvm
int main(int Argc, char **Argv) {
using namespace llvm;
cl::ParseCommandLineOptions(Argc, Argv, "");
exegesis::ExitOnErr.setExitCodeMapper([](const Error &Err) {
if (Err.isA<exegesis::ClusteringError>())
return EXIT_SUCCESS;
return EXIT_FAILURE;
});
if (exegesis::BenchmarkMode == exegesis::InstructionBenchmark::Unknown) {
exegesis::analysisMain();
} else {
exegesis::benchmarkMain();
}
return EXIT_SUCCESS;
}
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