bench.cpp

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// Copyright (c) 2015 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <bench/bench.h>
#include <bench/perf.h>

#include <assert.h>
#include <iostream>
#include <iomanip>

benchmark::BenchRunner::BenchmarkMap &benchmark::BenchRunner::benchmarks() {
    static std::map<std::string, benchmark::BenchFunction> benchmarks_map;
    return benchmarks_map;
}

benchmark::BenchRunner::BenchRunner(std::string name, benchmark::BenchFunction func)
{
    benchmarks().insert(std::make_pair(name, func));
}

void
benchmark::BenchRunner::RunAll(benchmark::duration elapsedTimeForOne)
{
    perf_init();
    if (std::ratio_less_equal<benchmark::clock::period, std::micro>::value) {
        std::cerr << "WARNING: Clock precision is worse than microsecond - benchmarks may be less accurate!\n";
    }
    std::cout << "#Benchmark" << "," << "count" << "," << "min(ns)" << "," << "max(ns)" << "," << "average(ns)" << ","
              << "min_cycles" << "," << "max_cycles" << "," << "average_cycles" << "\n";

    for (const auto &p: benchmarks()) {
        State state(p.first, elapsedTimeForOne);
        p.second(state);
    }
    perf_fini();
}

bool benchmark::State::KeepRunning()
{
    if (count & countMask) {
      ++count;
      return true;
    }
    time_point now;

    uint64_t nowCycles;
    if (count == 0) {
        lastTime = beginTime = now = clock::now();
        lastCycles = beginCycles = nowCycles = perf_cpucycles();
    }
    else {
        now = clock::now();
        auto elapsed = now - lastTime;
        auto elapsedOne = elapsed / (countMask + 1);
        if (elapsedOne < minTime) minTime = elapsedOne;
        if (elapsedOne > maxTime) maxTime = elapsedOne;

        // We only use relative values, so don't have to handle 64-bit wrap-around specially
        nowCycles = perf_cpucycles();
        uint64_t elapsedOneCycles = (nowCycles - lastCycles) / (countMask + 1);
        if (elapsedOneCycles < minCycles) minCycles = elapsedOneCycles;
        if (elapsedOneCycles > maxCycles) maxCycles = elapsedOneCycles;

        if (elapsed*128 < maxElapsed) {
          // If the execution was much too fast (1/128th of maxElapsed), increase the count mask by 8x and restart timing.
          // The restart avoids including the overhead of this code in the measurement.
          countMask = ((countMask<<3)|7) & ((1LL<<60)-1);
          count = 0;
          minTime = duration::max();
          maxTime = duration::zero();
          minCycles = std::numeric_limits<uint64_t>::max();
          maxCycles = std::numeric_limits<uint64_t>::min();
          return true;
        }
        if (elapsed*16 < maxElapsed) {
          uint64_t newCountMask = ((countMask<<1)|1) & ((1LL<<60)-1);
          if ((count & newCountMask)==0) {
              countMask = newCountMask;
          }
        }
    }
    lastTime = now;
    lastCycles = nowCycles;
    ++count;

    if (now - beginTime < maxElapsed) return true; // Keep going

    --count;

    assert(count != 0 && "count == 0 => (now == 0 && beginTime == 0) => return above");

    // Output results
    // Duration casts are only necessary here because hardware with sub-nanosecond clocks
    // will lose precision.
    int64_t min_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(minTime).count();
    int64_t max_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(maxTime).count();
    int64_t avg_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>((now-beginTime)/count).count();
    int64_t averageCycles = (nowCycles-beginCycles)/count;
    std::cout << std::fixed << std::setprecision(15) << name << "," << count << "," << min_elapsed << "," << max_elapsed << "," << avg_elapsed << ","
              << minCycles << "," << maxCycles << "," << averageCycles << "\n";
    std::cout.copyfmt(std::ios(nullptr));

    return false;
}