src/bench/bench.cpp

   1 // Copyright (c) 2015-2016 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #include <bench/bench.h>
   6 #include <bench/perf.h>
   7
   8 #include <assert.h>
   9 #include <iostream>
  10 #include <iomanip>
  11
  12 benchmark::BenchRunner::BenchmarkMap &benchmark::BenchRunner::benchmarks() {
  13     static std::map<std::string, benchmark::BenchFunction> benchmarks_map;
  14     return benchmarks_map;
  15 }
  16
  17 benchmark::BenchRunner::BenchRunner(std::string name, benchmark::BenchFunction func)
  18 {
  19     benchmarks().insert(std::make_pair(name, func));
  20 }
  21
  22 void
  23 benchmark::BenchRunner::RunAll(benchmark::duration elapsedTimeForOne)
  24 {
  25     perf_init();
  26     if (std::ratio_less_equal<benchmark::clock::period, std::micro>::value) {
  27         std::cerr << "WARNING: Clock precision is worse than microsecond - benchmarks may be less accurate!\n";
  28     }
  29     std::cout << "#Benchmark" << "," << "count" << "," << "min(ns)" << "," << "max(ns)" << "," << "average(ns)" << ","
  30               << "min_cycles" << "," << "max_cycles" << "," << "average_cycles" << "\n";
  31
  32     for (const auto &p: benchmarks()) {
  33         State state(p.first, elapsedTimeForOne);
  34         p.second(state);
  35     }
  36     perf_fini();
  37 }
  38
  39 bool benchmark::State::KeepRunning()
  40 {
  41     if (count & countMask) {
  42       ++count;
  43       return true;
  44     }
  45     time_point now;
  46
  47     uint64_t nowCycles;
  48     if (count == 0) {
  49         lastTime = beginTime = now = clock::now();
  50         lastCycles = beginCycles = nowCycles = perf_cpucycles();
  51     }
  52     else {
  53         now = clock::now();
  54         auto elapsed = now - lastTime;
  55         auto elapsedOne = elapsed / (countMask + 1);
  56         if (elapsedOne < minTime) minTime = elapsedOne;
  57         if (elapsedOne > maxTime) maxTime = elapsedOne;
  58
  59         // We only use relative values, so don't have to handle 64-bit wrap-around specially
  60         nowCycles = perf_cpucycles();
  61         uint64_t elapsedOneCycles = (nowCycles - lastCycles) / (countMask + 1);
  62         if (elapsedOneCycles < minCycles) minCycles = elapsedOneCycles;
  63         if (elapsedOneCycles > maxCycles) maxCycles = elapsedOneCycles;
  64
  65         if (elapsed*128 < maxElapsed) {
  66           // If the execution was much too fast (1/128th of maxElapsed), increase the count mask by 8x and restart timing.
  67           // The restart avoids including the overhead of this code in the measurement.
  68           countMask = ((countMask<<3)|7) & ((1LL<<60)-1);
  69           count = 0;
  70           minTime = duration::max();
  71           maxTime = duration::zero();
  72           minCycles = std::numeric_limits<uint64_t>::max();
  73           maxCycles = std::numeric_limits<uint64_t>::min();
  74           return true;
  75         }
  76         if (elapsed*16 < maxElapsed) {
  77           uint64_t newCountMask = ((countMask<<1)|1) & ((1LL<<60)-1);
  78           if ((count & newCountMask)==0) {
  79               countMask = newCountMask;
  80           }
  81         }
  82     }
  83     lastTime = now;
  84     lastCycles = nowCycles;
  85     ++count;
  86
  87     if (now - beginTime < maxElapsed) return true; // Keep going
  88
  89     --count;
  90
  91     assert(count != 0 && "count == 0 => (now == 0 && beginTime == 0) => return above");
  92
  93     // Output results
  94     // Duration casts are only necessary here because hardware with sub-nanosecond clocks
  95     // will lose precision.
  96     int64_t min_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(minTime).count();
  97     int64_t max_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(maxTime).count();
  98     int64_t avg_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>((now-beginTime)/count).count();
  99     int64_t averageCycles = (nowCycles-beginCycles)/count;
 100     std::cout << std::fixed << std::setprecision(15) << name << "," << count << "," << min_elapsed << "," << max_elapsed << "," << avg_elapsed << ","
 101               << minCycles << "," << maxCycles << "," << averageCycles << "\n";
 102     std::cout.copyfmt(std::ios(nullptr));
 103
 104     return false;
 105 }