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rocksdb/util/benchharness.cc

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
// This code is derived from Benchmark.cpp implemented in Folly, the opensourced
// Facebook C++ library available at https://github.com/facebook/folly
// The code has removed any dependence on other folly and boost libraries
#include "util/benchharness.h"
#include <algorithm>
#include <cmath>
#include <cstring>
#include <limits>
#include <string>
#include <utility>
#include <vector>
using std::function;
using std::get;
using std::make_pair;
using std::max;
using std::min;
using std::pair;
using std::sort;
using std::string;
using std::tuple;
using std::vector;
DEFINE_bool(benchmark, false, "Run benchmarks.");
DEFINE_uint64(bm_min_usec, 100,
"Minimum # of microseconds we'll accept for each benchmark.");
DEFINE_int64(bm_min_iters, 1,
"Minimum # of iterations we'll try for each benchmark.");
DEFINE_int32(bm_max_secs, 1,
"Maximum # of seconds we'll spend on each benchmark.");
namespace rocksdb {
namespace benchmark {
BenchmarkSuspender::NanosecondsSpent BenchmarkSuspender::nsSpent;
typedef function<uint64_t(unsigned int)> BenchmarkFun;
static vector<tuple<const char*, const char*, BenchmarkFun>> benchmarks;
// Add the global baseline
BENCHMARK(globalBenchmarkBaseline) {
asm volatile("");
}
void detail::AddBenchmarkImpl(const char* file, const char* name,
BenchmarkFun fun) {
benchmarks.emplace_back(file, name, std::move(fun));
}
/**
* Given a point, gives density at that point as a number 0.0 < x <=
* 1.0. The result is 1.0 if all samples are equal to where, and
* decreases near 0 if all points are far away from it. The density is
* computed with the help of a radial basis function.
*/
static double Density(const double * begin, const double *const end,
const double where, const double bandwidth) {
assert(begin < end);
assert(bandwidth > 0.0);
double sum = 0.0;
for (auto i = begin; i < end; i++) {
auto d = (*i - where) / bandwidth;
sum += exp(- d * d);
}
return sum / (end - begin);
}
/**
* Computes mean and variance for a bunch of data points. Note that
* mean is currently not being used.
*/
static pair<double, double>
MeanVariance(const double * begin, const double *const end) {
assert(begin < end);
double sum = 0.0, sum2 = 0.0;
for (auto i = begin; i < end; i++) {
sum += *i;
sum2 += *i * *i;
}
auto const n = end - begin;
return make_pair(sum / n, sqrt((sum2 - sum * sum / n) / n));
}
/**
* Computes the mode of a sample set through brute force. Assumes
* input is sorted.
*/
static double Mode(const double * begin, const double *const end) {
assert(begin < end);
// Lower bound and upper bound for result and their respective
// densities.
auto
result = 0.0,
bestDensity = 0.0;
// Get the variance so we pass it down to Density()
auto const sigma = MeanVariance(begin, end).second;
if (!sigma) {
// No variance means constant signal
return *begin;
}
for (auto i = begin; i < end; i++) {
assert(i == begin || *i >= i[-1]);
auto candidate = Density(begin, end, *i, sigma * sqrt(2.0));
if (candidate > bestDensity) {
// Found a new best
bestDensity = candidate;
result = *i;
} else {
// Density is decreasing... we could break here if we definitely
// knew this is unimodal.
}
}
return result;
}
/**
* Given a bunch of benchmark samples, estimate the actual run time.
*/
static double EstimateTime(double * begin, double * end) {
assert(begin < end);
// Current state of the art: get the minimum. After some
// experimentation, it seems taking the minimum is the best.
return *std::min_element(begin, end);
// What follows after estimates the time as the mode of the
// distribution.
// Select the awesomest (i.e. most frequent) result. We do this by
// sorting and then computing the longest run length.
sort(begin, end);
// Eliminate outliers. A time much larger than the minimum time is
// considered an outlier.
while (end[-1] > 2.0 * *begin) {
--end;
if (begin == end) {
// LOG(INFO) << *begin;
}
assert(begin < end);
}
double result = 0;
/* Code used just for comparison purposes */ {
unsigned bestFrequency = 0;
unsigned candidateFrequency = 1;
double candidateValue = *begin;
for (auto current = begin + 1; ; ++current) {
if (current == end || *current != candidateValue) {
// Done with the current run, see if it was best
if (candidateFrequency > bestFrequency) {
bestFrequency = candidateFrequency;
result = candidateValue;
}
if (current == end) {
break;
}
// Start a new run
candidateValue = *current;
candidateFrequency = 1;
} else {
// Cool, inside a run, increase the frequency
++candidateFrequency;
}
}
}
result = Mode(begin, end);
return result;
}
static double RunBenchmarkGetNSPerIteration(const BenchmarkFun& fun,
const double globalBaseline) {
// They key here is accuracy; too low numbers means the accuracy was
// coarse. We up the ante until we get to at least minNanoseconds
// timings.
static const auto minNanoseconds = FLAGS_bm_min_usec * 1000UL;
// We do measurements in several epochs and take the minimum, to
// account for jitter.
static const unsigned int epochs = 1000;
// We establish a total time budget as we don't want a measurement
// to take too long. This will curtail the number of actual epochs.
const uint64_t timeBudgetInNs = FLAGS_bm_max_secs * 1000000000;
auto env = Env::Default();
uint64_t global = env->NowNanos();
double epochResults[epochs] = { 0 };
size_t actualEpochs = 0;
for (; actualEpochs < epochs; ++actualEpochs) {
for (unsigned int n = static_cast<unsigned int>(FLAGS_bm_min_iters);
n < (1UL << 30); n *= 2) {
auto const nsecs = fun(n);
if (nsecs < minNanoseconds) {
continue;
}
// We got an accurate enough timing, done. But only save if
// smaller than the current result.
epochResults[actualEpochs] = max(0.0,
static_cast<double>(nsecs) / n - globalBaseline);
// Done with the current epoch, we got a meaningful timing.
break;
}
uint64_t now = env->NowNanos();
if ((now - global) >= timeBudgetInNs) {
// No more time budget available.
++actualEpochs;
break;
}
}
// If the benchmark was basically drowned in baseline noise, it's
// possible it became negative.
return max(0.0, EstimateTime(epochResults, epochResults + actualEpochs));
}
struct ScaleInfo {
double boundary;
const char* suffix;
};
static const ScaleInfo kTimeSuffixes[] {
{ 365.25 * 24 * 3600, "years" },
{ 24 * 3600, "days" },
{ 3600, "hr" },
{ 60, "min" },
{ 1, "s" },
{ 1E-3, "ms" },
{ 1E-6, "us" },
{ 1E-9, "ns" },
{ 1E-12, "ps" },
{ 1E-15, "fs" },
{ 0, nullptr },
};
static const ScaleInfo kMetricSuffixes[] {
{ 1E24, "Y" }, // yotta
{ 1E21, "Z" }, // zetta
{ 1E18, "X" }, // "exa" written with suffix 'X' so as to not create
// confusion with scientific notation
{ 1E15, "P" }, // peta
{ 1E12, "T" }, // terra
{ 1E9, "G" }, // giga
{ 1E6, "M" }, // mega
{ 1E3, "K" }, // kilo
{ 1, "" },
{ 1E-3, "m" }, // milli
{ 1E-6, "u" }, // micro
{ 1E-9, "n" }, // nano
{ 1E-12, "p" }, // pico
{ 1E-15, "f" }, // femto
{ 1E-18, "a" }, // atto
{ 1E-21, "z" }, // zepto
{ 1E-24, "y" }, // yocto
{ 0, nullptr },
};
static string HumanReadable(double n, unsigned int decimals,
const ScaleInfo* scales) {
if (std::isinf(n) || std::isnan(n)) {
return std::to_string(n);
}
const double absValue = fabs(n);
const ScaleInfo* scale = scales;
while (absValue < scale[0].boundary && scale[1].suffix != nullptr) {
++scale;
}
const double scaledValue = n / scale->boundary;
char a[80];
snprintf(a, sizeof(a), "%.*f%s", decimals, scaledValue, scale->suffix);
return a;
}
static string ReadableTime(double n, unsigned int decimals) {
return HumanReadable(n, decimals, kTimeSuffixes);
}
static string MetricReadable(double n, unsigned int decimals) {
return HumanReadable(n, decimals, kMetricSuffixes);
}
static void PrintBenchmarkResultsAsTable(
const vector<tuple<const char*, const char*, double> >& data) {
// Width available
static const uint columns = 76;
// Compute the longest benchmark name
size_t longestName = 0;
for (size_t i = 1; i < benchmarks.size(); i++) {
longestName = max(longestName, strlen(get<1>(benchmarks[i])));
}
// Print a horizontal rule
auto separator = [&](char pad) {
puts(string(columns, pad).c_str());
};
// Print header for a file
auto header = [&](const char* file) {
separator('=');
printf("%-*srelative time/iter iters/s\n",
columns - 28, file);
separator('=');
};
double baselineNsPerIter = std::numeric_limits<double>::max();
const char* lastFile = "";
for (auto& datum : data) {
auto file = get<0>(datum);
if (strcmp(file, lastFile)) {
// New file starting
header(file);
lastFile = file;
}
string s = get<1>(datum);
if (s == "-") {
separator('-');
continue;
}
bool useBaseline /* = void */;
if (s[0] == '%') {
s.erase(0, 1);
useBaseline = true;
} else {
baselineNsPerIter = get<2>(datum);
useBaseline = false;
}
s.resize(columns - 29, ' ');
auto nsPerIter = get<2>(datum);
auto secPerIter = nsPerIter / 1E9;
auto itersPerSec = 1 / secPerIter;
if (!useBaseline) {
// Print without baseline
printf("%*s %9s %7s\n",
static_cast<int>(s.size()), s.c_str(),
ReadableTime(secPerIter, 2).c_str(),
MetricReadable(itersPerSec, 2).c_str());
} else {
// Print with baseline
auto rel = baselineNsPerIter / nsPerIter * 100.0;
printf("%*s %7.2f%% %9s %7s\n",
static_cast<int>(s.size()), s.c_str(),
rel,
ReadableTime(secPerIter, 2).c_str(),
MetricReadable(itersPerSec, 2).c_str());
}
}
separator('=');
}
void RunBenchmarks() {
ASSERT_TRUE(!benchmarks.empty());
vector<tuple<const char*, const char*, double>> results;
results.reserve(benchmarks.size() - 1);
// PLEASE KEEP QUIET. MEASUREMENTS IN PROGRESS.
auto const globalBaseline = RunBenchmarkGetNSPerIteration(
get<2>(benchmarks.front()), 0);
for (size_t i = 1; i < benchmarks.size(); i++) {
double elapsed = 0.0;
if (strcmp(get<1>(benchmarks[i]), "-") != 0) { // skip separators
elapsed = RunBenchmarkGetNSPerIteration(get<2>(benchmarks[i]),
globalBaseline);
}
results.emplace_back(get<0>(benchmarks[i]),
get<1>(benchmarks[i]), elapsed);
}
// PLEASE MAKE NOISE. MEASUREMENTS DONE.
PrintBenchmarkResultsAsTable(results);
}
} // namespace benchmark
} // namespace rocksdb