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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
#include "opentelemetry/common/spin_lock_mutex.h"
#include <benchmark/benchmark.h>
#include <mutex>
namespace
{
using opentelemetry::common::SpinLockMutex;
constexpr int TightLoopLocks = 10000;
// Runs a thrash-test where we spin up N threads, each of which will
// attempt to lock-mutate-unlock a total of `TightLoopLocks` times.
//
// lock: A lambda denoting how to lock. Accepts a reference to `SpinLockType`.
// unlock: A lambda denoting how to unlock. Accepts a reference to `SpinLockType`.
template <typename SpinLockType, typename LockF, typename UnlockF>
inline void SpinThrash(benchmark::State &s, SpinLockType &spinlock, LockF lock, UnlockF unlock)
{
auto num_threads = s.range(0);
// Value we will increment, fighting over a spinlock.
// The contention is meant to be brief, as close to our expected
// use cases of "updating pointers" or "pushing an event onto a buffer".
std::int64_t value = 0;
std::vector<std::thread> threads;
threads.reserve(num_threads);
// Timing loop
for (auto _ : s)
{
for (auto i = 0; i < num_threads; i++)
{
threads.emplace_back([&] {
// Increment value once each time the lock is acquired. Spin a few times
// to ensure maximum thread contention.
for (int i = 0; i < TightLoopLocks; i++)
{
lock(spinlock);
value++;
unlock(spinlock);
}
});
}
// Join threads
for (auto &thread : threads)
thread.join();
threads.clear();
}
}
// Benchmark of full spin-lock implementation.
static void BM_SpinLockThrashing(benchmark::State &s)
{
SpinLockMutex spinlock;
SpinThrash(
s, spinlock, [](SpinLockMutex &m) { m.lock(); }, [](SpinLockMutex &m) { m.unlock(); });
}
// Naive `while(try_lock()) {}` implementation of lock.
static void BM_NaiveSpinLockThrashing(benchmark::State &s)
{
SpinLockMutex spinlock;
SpinThrash(
s, spinlock,
[](SpinLockMutex &m) {
while (!m.try_lock())
{
// Left this comment to keep the same format on old and new versions of clang-format
}
},
[](SpinLockMutex &m) { m.unlock(); });
}
// Simple `while(try_lock()) { yield-processor }`
static void BM_ProcYieldSpinLockThrashing(benchmark::State &s)
{
SpinLockMutex spinlock;
SpinThrash<SpinLockMutex>(
s, spinlock,
[](SpinLockMutex &m) {
while (!m.try_lock())
{
#if defined(_MSC_VER)
YieldProcessor();
#elif defined(__i386__) || defined(__x86_64__)
# if defined(__clang__)
_mm_pause();
# else
__builtin_ia32_pause();
# endif
#elif defined(__arm__)
__asm__ volatile("yield" ::: "memory");
#endif
}
},
[](SpinLockMutex &m) { m.unlock(); });
}
// SpinLock thrashing with thread::yield().
static void BM_ThreadYieldSpinLockThrashing(benchmark::State &s)
{
std::atomic_flag mutex = ATOMIC_FLAG_INIT;
SpinThrash<std::atomic_flag>(
s, mutex,
[](std::atomic_flag &l) {
uint32_t try_count = 0;
while (l.test_and_set(std::memory_order_acq_rel))
{
++try_count;
if (try_count % 32)
{
std::this_thread::yield();
}
}
std::this_thread::yield();
},
[](std::atomic_flag &l) { l.clear(std::memory_order_release); });
}
// Run the benchmarks at 2x thread/core and measure the amount of time to thrash around.
BENCHMARK(BM_SpinLockThrashing)
->RangeMultiplier(2)
->Range(1, std::thread::hardware_concurrency())
->MeasureProcessCPUTime()
->UseRealTime()
->Unit(benchmark::kMillisecond);
BENCHMARK(BM_ProcYieldSpinLockThrashing)
->RangeMultiplier(2)
->Range(1, std::thread::hardware_concurrency())
->MeasureProcessCPUTime()
->UseRealTime()
->Unit(benchmark::kMillisecond);
BENCHMARK(BM_NaiveSpinLockThrashing)
->RangeMultiplier(2)
->Range(1, std::thread::hardware_concurrency())
->MeasureProcessCPUTime()
->UseRealTime()
->Unit(benchmark::kMillisecond);
BENCHMARK(BM_ThreadYieldSpinLockThrashing)
->RangeMultiplier(2)
->Range(1, std::thread::hardware_concurrency())
->MeasureProcessCPUTime()
->UseRealTime()
->Unit(benchmark::kMillisecond);
} // namespace
BENCHMARK_MAIN();
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