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bench: Add support for measuring CPU cycles

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This adds cycle min/max/avg to the statistics.

Supported on x86 and x86_64 (natively through rdtsc), as well as Linux
(perf syscall).
This commit is contained in:
Wladimir J. van der Laan
2016-11-22 10:22:08 +01:00
parent 55b2eddcc8
commit 3532818746
5 changed files with 121 additions and 5 deletions
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22
src/bench/bench.cpp
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@@ -3,6 +3,7 @@
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include "bench.h"
#include "perf.h"
#include <iostream>
#include <iomanip>
@@ -26,7 +27,9 @@ BenchRunner::BenchRunner(std::string name, BenchFunction func)
void
BenchRunner::RunAll(double elapsedTimeForOne)
{
std::cout << "#Benchmark" << "," << "count" << "," << "min" << "," << "max" << "," << "average" << "\n";
perf_init();
std::cout << "#Benchmark" << "," << "count" << "," << "min" << "," << "max" << "," << "average" << ","
<< "min_cycles" << "," << "max_cycles" << "," << "average_cycles" << "\n";
for (std::map<std::string,BenchFunction>::iterator it = benchmarks.begin();
it != benchmarks.end(); ++it) {
@@ -35,6 +38,7 @@ BenchRunner::RunAll(double elapsedTimeForOne)
BenchFunction& func = it->second;
func(state);
}
perf_fini();
}
bool State::KeepRunning()
@@ -44,8 +48,10 @@ bool State::KeepRunning()
return true;
}
double now;
uint64_t nowCycles;
if (count == 0) {
lastTime = beginTime = now = gettimedouble();
lastCycles = beginCycles = nowCycles = perf_cpucycles();
}
else {
now = gettimedouble();
@@ -53,6 +59,13 @@ bool State::KeepRunning()
double elapsedOne = elapsed * countMaskInv;
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) * countMaskInv;
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.
@@ -61,6 +74,8 @@ bool State::KeepRunning()
count = 0;
minTime = std::numeric_limits<double>::max();
maxTime = std::numeric_limits<double>::min();
minCycles = std::numeric_limits<uint64_t>::max();
maxCycles = std::numeric_limits<uint64_t>::min();
return true;
}
if (elapsed*16 < maxElapsed) {
@@ -72,6 +87,7 @@ bool State::KeepRunning()
}
}
lastTime = now;
lastCycles = nowCycles;
++count;
if (now - beginTime < maxElapsed) return true; // Keep going
@@ -80,7 +96,9 @@ bool State::KeepRunning()
// Output results
double average = (now-beginTime)/count;
std::cout << std::fixed << std::setprecision(15) << name << "," << count << "," << minTime << "," << maxTime << "," << average << "\n";
int64_t averageCycles = (nowCycles-beginCycles)/count;
std::cout << std::fixed << std::setprecision(15) << name << "," << count << "," << minTime << "," << maxTime << "," << average << ","
<< minCycles << "," << maxCycles << "," << averageCycles << "\n";
return false;
}