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bench: switch to std::chrono for time measurements

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std::chrono removes portability issues.

Rather than storing doubles, store the untouched time_points. Then
convert to nanoseconds for display. This allows for maximum precision, while
keeping results comparable between differing hardware/operating systems.

Also, display full nanosecond counts rather than sub-second floats.
This commit is contained in:
Cory Fields
2017-10-25 16:38:24 -04:00
parent 57ee73990f
commit c515d266ec
3 changed files with 31 additions and 29 deletions
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34
src/bench/bench.cpp
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@@ -8,29 +8,22 @@
#include <assert.h>
#include <iostream>
#include <iomanip>
#include <sys/time.h>
benchmark::BenchRunner::BenchmarkMap &benchmark::BenchRunner::benchmarks() {
static std::map<std::string, benchmark::BenchFunction> benchmarks_map;
return benchmarks_map;
}
static double gettimedouble(void) {
struct timeval tv;
gettimeofday(&tv, nullptr);
return tv.tv_usec * 0.000001 + tv.tv_sec;
}
benchmark::BenchRunner::BenchRunner(std::string name, benchmark::BenchFunction func)
{
benchmarks().insert(std::make_pair(name, func));
}
void
benchmark::BenchRunner::RunAll(double elapsedTimeForOne)
benchmark::BenchRunner::RunAll(benchmark::duration elapsedTimeForOne)
{
perf_init();
std::cout << "#Benchmark" << "," << "count" << "," << "min" << "," << "max" << "," << "average" << ","
std::cout << "#Benchmark" << "," << "count" << "," << "min(ns)" << "," << "max(ns)" << "," << "average(ns)" << ","
<< "min_cycles" << "," << "max_cycles" << "," << "average_cycles" << "\n";
for (const auto &p: benchmarks()) {
@@ -46,16 +39,17 @@ bool benchmark::State::KeepRunning()
++count;
return true;
}
double now;
time_point now;
uint64_t nowCycles;
if (count == 0) {
lastTime = beginTime = now = gettimedouble();
lastTime = beginTime = now = clock::now();
lastCycles = beginCycles = nowCycles = perf_cpucycles();
}
else {
now = gettimedouble();
double elapsed = now - lastTime;
double elapsedOne = elapsed / (countMask + 1);
now = clock::now();
auto elapsed = now - lastTime;
auto elapsedOne = elapsed / (countMask + 1);
if (elapsedOne < minTime) minTime = elapsedOne;
if (elapsedOne > maxTime) maxTime = elapsedOne;
@@ -70,8 +64,8 @@ bool benchmark::State::KeepRunning()
// The restart avoids including the overhead of this code in the measurement.
countMask = ((countMask<<3)|7) & ((1LL<<60)-1);
count = 0;
minTime = std::numeric_limits<double>::max();
maxTime = std::numeric_limits<double>::min();
minTime = duration::max();
maxTime = duration::zero();
minCycles = std::numeric_limits<uint64_t>::max();
maxCycles = std::numeric_limits<uint64_t>::min();
return true;
@@ -94,9 +88,13 @@ bool benchmark::State::KeepRunning()
assert(count != 0 && "count == 0 => (now == 0 && beginTime == 0) => return above");
// Output results
double average = (now-beginTime)/count;
// 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 << "," << minTime << "," << maxTime << "," << average << ","
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));