/*
- * Copyright 2016 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#include <folly/ScopeGuard.h>
#include <folly/Traits.h>
#include <folly/portability/GFlags.h>
-#include <folly/portability/Time.h>
#include <cassert>
-#include <ctime>
-#include <boost/function_types/function_arity.hpp>
+#include <chrono>
#include <functional>
-#include <glog/logging.h>
#include <limits>
#include <type_traits>
+#include <boost/function_types/function_arity.hpp>
+#include <glog/logging.h>
+
DECLARE_bool(benchmark);
namespace folly {
namespace detail {
-typedef std::pair<uint64_t, unsigned int> TimeIterPair;
+using TimeIterPair =
+ std::pair<std::chrono::high_resolution_clock::duration, unsigned int>;
/**
* Adds a benchmark wrapped in a std::function. Only used
const char* name,
std::function<TimeIterPair(unsigned int)>);
-/**
- * Takes the difference between two timespec values. end is assumed to
- * occur after start.
- */
-inline uint64_t timespecDiff(timespec end, timespec start) {
- if (end.tv_sec == start.tv_sec) {
- assert(end.tv_nsec >= start.tv_nsec);
- return end.tv_nsec - start.tv_nsec;
- }
- assert(end.tv_sec > start.tv_sec);
- auto diff = uint64_t(end.tv_sec - start.tv_sec);
- assert(diff <
- std::numeric_limits<uint64_t>::max() / 1000000000UL);
- return diff * 1000000000UL
- + end.tv_nsec - start.tv_nsec;
-}
-
-/**
- * Takes the difference between two sets of timespec values. The first
- * two come from a high-resolution clock whereas the other two come
- * from a low-resolution clock. The crux of the matter is that
- * high-res values may be bogus as documented in
- * http://linux.die.net/man/3/clock_gettime. The trouble is when the
- * running process migrates from one CPU to another, which is more
- * likely for long-running processes. Therefore we watch for high
- * differences between the two timings.
- *
- * This function is subject to further improvements.
- */
-inline uint64_t timespecDiff(timespec end, timespec start,
- timespec endCoarse, timespec startCoarse) {
- auto fine = timespecDiff(end, start);
- auto coarse = timespecDiff(endCoarse, startCoarse);
- if (coarse - fine >= 1000000) {
- // The fine time is in all likelihood bogus
- return coarse;
- }
- return fine;
-}
-
} // namespace detail
/**
* Supporting type for BENCHMARK_SUSPEND defined below.
*/
struct BenchmarkSuspender {
+ using Clock = std::chrono::high_resolution_clock;
+ using TimePoint = Clock::time_point;
+ using Duration = Clock::duration;
+
BenchmarkSuspender() {
- CHECK_EQ(0, clock_gettime(CLOCK_REALTIME, &start));
+ start = Clock::now();
}
BenchmarkSuspender(const BenchmarkSuspender &) = delete;
BenchmarkSuspender(BenchmarkSuspender && rhs) noexcept {
start = rhs.start;
- rhs.start.tv_nsec = rhs.start.tv_sec = 0;
+ rhs.start = {};
}
BenchmarkSuspender& operator=(const BenchmarkSuspender &) = delete;
BenchmarkSuspender& operator=(BenchmarkSuspender && rhs) {
- if (start.tv_nsec > 0 || start.tv_sec > 0) {
+ if (start != TimePoint{}) {
tally();
}
start = rhs.start;
- rhs.start.tv_nsec = rhs.start.tv_sec = 0;
+ rhs.start = {};
return *this;
}
~BenchmarkSuspender() {
- if (start.tv_nsec > 0 || start.tv_sec > 0) {
+ if (start != TimePoint{}) {
tally();
}
}
void dismiss() {
- assert(start.tv_nsec > 0 || start.tv_sec > 0);
+ assert(start != TimePoint{});
tally();
- start.tv_nsec = start.tv_sec = 0;
+ start = {};
}
void rehire() {
- assert(start.tv_nsec == 0 || start.tv_sec == 0);
- CHECK_EQ(0, clock_gettime(CLOCK_REALTIME, &start));
+ assert(start == TimePoint{});
+ start = Clock::now();
}
template <class F>
}
/**
- * Accumulates nanoseconds spent outside benchmark.
+ * Accumulates time spent outside benchmark.
*/
- typedef uint64_t NanosecondsSpent;
- static NanosecondsSpent nsSpent;
+ static Duration timeSpent;
-private:
+ private:
void tally() {
- timespec end;
- CHECK_EQ(0, clock_gettime(CLOCK_REALTIME, &end));
- nsSpent += detail::timespecDiff(end, start);
+ auto end = Clock::now();
+ timeSpent += end - start;
start = end;
}
- timespec start;
+ TimePoint start;
};
/**
>::type
addBenchmark(const char* file, const char* name, Lambda&& lambda) {
auto execute = [=](unsigned int times) {
- BenchmarkSuspender::nsSpent = 0;
- timespec start, end;
+ BenchmarkSuspender::timeSpent = {};
unsigned int niter;
// CORE MEASUREMENT STARTS
- auto const r1 = clock_gettime(CLOCK_REALTIME, &start);
+ auto start = std::chrono::high_resolution_clock::now();
niter = lambda(times);
- auto const r2 = clock_gettime(CLOCK_REALTIME, &end);
+ auto end = std::chrono::high_resolution_clock::now();
// CORE MEASUREMENT ENDS
- CHECK_EQ(0, r1);
- CHECK_EQ(0, r2);
-
return detail::TimeIterPair(
- detail::timespecDiff(end, start) - BenchmarkSuspender::nsSpent,
- niter);
+ (end - start) - BenchmarkSuspender::timeSpent, niter);
};
detail::addBenchmarkImpl(file, name,
template <typename T>
auto doNotOptimizeAway(const T& datum) -> typename std::enable_if<
!detail::DoNotOptimizeAwayNeedsIndirect<T>::value>::type {
- asm volatile("" ::"X"(datum));
+ // The "r" constraint forces the compiler to make datum available
+ // in a register to the asm block, which means that it must have
+ // computed/loaded it. We use this path for things that are <=
+ // sizeof(long) (they have to fit), trivial (otherwise the compiler
+ // doesn't want to put them in a register), and not a pointer (because
+ // doNotOptimizeAway(&foo) would otherwise be a foot gun that didn't
+ // necessarily compute foo).
+ //
+ // An earlier version of this method had a more permissive input operand
+ // constraint, but that caused unnecessary variation between clang and
+ // gcc benchmarks.
+ asm volatile("" ::"r"(datum));
}
template <typename T>
auto doNotOptimizeAway(const T& datum) -> typename std::enable_if<
detail::DoNotOptimizeAwayNeedsIndirect<T>::value>::type {
+ // This version of doNotOptimizeAway tells the compiler that the asm
+ // block will read datum from memory, and that in addition it might read
+ // or write from any memory location. If the memory clobber could be
+ // separated into input and output that would be preferrable.
asm volatile("" ::"m"(datum) : "memory");
}
projects / folly.git / blobdiff