llvm/tools/llvm-exegesis/lib/LatencyBenchmarkRunner.cpp

   1 //===-- LatencyBenchmarkRunner.cpp ------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "LatencyBenchmarkRunner.h"
  10
  11 #include "Target.h"
  12 #include "BenchmarkRunner.h"
  13
  14 namespace llvm {
  15 namespace exegesis {
  16
  17 LatencyBenchmarkRunner::LatencyBenchmarkRunner(const LLVMState &State,
  18                                                InstructionBenchmark::ModeE Mode)
  19     : BenchmarkRunner(State, Mode) {
  20   assert((Mode == InstructionBenchmark::Latency ||
  21           Mode == InstructionBenchmark::InverseThroughput) &&
  22          "invalid mode");
  23 }
  24
  25 LatencyBenchmarkRunner::~LatencyBenchmarkRunner() = default;
  26
  27 Expected<std::vector<BenchmarkMeasure>> LatencyBenchmarkRunner::runMeasurements(
  28     const FunctionExecutor &Executor) const {
  29   // Cycle measurements include some overhead from the kernel. Repeat the
  30   // measure several times and take the minimum value.
  31   constexpr const int NumMeasurements = 30;
  32   int64_t MinValue = std::numeric_limits<int64_t>::max();
  33   const char *CounterName = State.getPfmCounters().CycleCounter;
  34   for (size_t I = 0; I < NumMeasurements; ++I) {
  35     auto ExpectedCounterValue = Executor.runAndMeasure(CounterName);
  36     if (!ExpectedCounterValue)
  37       return ExpectedCounterValue.takeError();
  38     if (*ExpectedCounterValue < MinValue)
  39       MinValue = *ExpectedCounterValue;
  40   }
  41   std::vector<BenchmarkMeasure> Result;
  42   switch (Mode) {
  43   case InstructionBenchmark::Latency:
  44     Result = {BenchmarkMeasure::Create("latency", MinValue)};
  45     break;
  46   case InstructionBenchmark::InverseThroughput:
  47     Result = {BenchmarkMeasure::Create("inverse_throughput", MinValue)};
  48     break;
  49   default:
  50     break;
  51   }
  52   return std::move(Result);
  53 }
  54
  55 } // namespace exegesis
  56 } // namespace llvm