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// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include <linux/futex.h>
#include <atomic>
#include <cerrno>
#include <cstdint>
#include <cstdlib>
#include <ctime>
#include "gtest/gtest.h"
#include "absl/time/clock.h"
#include "absl/time/time.h"
#include "benchmark/benchmark.h"
#include "test/util/logging.h"
#include "test/util/thread_util.h"
namespace gvisor {
namespace testing {
namespace {
inline int FutexWait(std::atomic<int32_t>* v, int32_t val) {
return syscall(SYS_futex, v, FUTEX_WAIT_PRIVATE, val, nullptr);
}
inline int FutexWaitMonotonicTimeout(std::atomic<int32_t>* v, int32_t val,
const struct timespec* timeout) {
return syscall(SYS_futex, v, FUTEX_WAIT_PRIVATE, val, timeout);
}
inline int FutexWaitMonotonicDeadline(std::atomic<int32_t>* v, int32_t val,
const struct timespec* deadline) {
return syscall(SYS_futex, v, FUTEX_WAIT_BITSET_PRIVATE, val, deadline,
nullptr, FUTEX_BITSET_MATCH_ANY);
}
inline int FutexWaitRealtimeDeadline(std::atomic<int32_t>* v, int32_t val,
const struct timespec* deadline) {
return syscall(SYS_futex, v, FUTEX_WAIT_BITSET_PRIVATE | FUTEX_CLOCK_REALTIME,
val, deadline, nullptr, FUTEX_BITSET_MATCH_ANY);
}
inline int FutexWake(std::atomic<int32_t>* v, int32_t count) {
return syscall(SYS_futex, v, FUTEX_WAKE_PRIVATE, count);
}
// This just uses FUTEX_WAKE on an address with nothing waiting, very simple.
void BM_FutexWakeNop(benchmark::State& state) {
std::atomic<int32_t> v(0);
for (auto _ : state) {
TEST_PCHECK(FutexWake(&v, 1) == 0);
}
}
BENCHMARK(BM_FutexWakeNop)->MinTime(5);
// This just uses FUTEX_WAIT on an address whose value has changed, i.e., the
// syscall won't wait.
void BM_FutexWaitNop(benchmark::State& state) {
std::atomic<int32_t> v(0);
for (auto _ : state) {
TEST_PCHECK(FutexWait(&v, 1) == -1 && errno == EAGAIN);
}
}
BENCHMARK(BM_FutexWaitNop)->MinTime(5);
// This uses FUTEX_WAIT with a timeout on an address whose value never
// changes, such that it always times out. Timeout overhead can be estimated by
// timer overruns for short timeouts.
void BM_FutexWaitMonotonicTimeout(benchmark::State& state) {
const absl::Duration timeout = absl::Nanoseconds(state.range(0));
std::atomic<int32_t> v(0);
auto ts = absl::ToTimespec(timeout);
for (auto _ : state) {
TEST_PCHECK(FutexWaitMonotonicTimeout(&v, 0, &ts) == -1 &&
errno == ETIMEDOUT);
}
}
BENCHMARK(BM_FutexWaitMonotonicTimeout)
->MinTime(5)
->UseRealTime()
->Arg(1)
->Arg(10)
->Arg(100)
->Arg(1000)
->Arg(10000);
// This uses FUTEX_WAIT_BITSET with a deadline that is in the past. This allows
// estimation of the overhead of setting up a timer for a deadline (as opposed
// to a timeout as specified for FUTEX_WAIT).
void BM_FutexWaitMonotonicDeadline(benchmark::State& state) {
std::atomic<int32_t> v(0);
struct timespec ts = {};
for (auto _ : state) {
TEST_PCHECK(FutexWaitMonotonicDeadline(&v, 0, &ts) == -1 &&
errno == ETIMEDOUT);
}
}
BENCHMARK(BM_FutexWaitMonotonicDeadline)->MinTime(5);
// This is equivalent to BM_FutexWaitMonotonicDeadline, but uses CLOCK_REALTIME
// instead of CLOCK_MONOTONIC for the deadline.
void BM_FutexWaitRealtimeDeadline(benchmark::State& state) {
std::atomic<int32_t> v(0);
struct timespec ts = {};
for (auto _ : state) {
TEST_PCHECK(FutexWaitRealtimeDeadline(&v, 0, &ts) == -1 &&
errno == ETIMEDOUT);
}
}
BENCHMARK(BM_FutexWaitRealtimeDeadline)->MinTime(5);
int64_t GetCurrentMonotonicTimeNanos() {
struct timespec ts;
TEST_CHECK(clock_gettime(CLOCK_MONOTONIC, &ts) != -1);
return ts.tv_sec * 1000000000ULL + ts.tv_nsec;
}
void SpinNanos(int64_t delay_ns) {
if (delay_ns <= 0) {
return;
}
const int64_t end = GetCurrentMonotonicTimeNanos() + delay_ns;
while (GetCurrentMonotonicTimeNanos() < end) {
// spin
}
}
// Each iteration of FutexRoundtripDelayed involves a thread sending a futex
// wakeup to another thread, which spins for delay_us and then sends a futex
// wakeup back. The time per iteration is 2 * (delay_us + kBeforeWakeDelayNs +
// futex/scheduling overhead).
void BM_FutexRoundtripDelayed(benchmark::State& state) {
const int delay_us = state.range(0);
const int64_t delay_ns = delay_us * 1000;
// Spin for an extra kBeforeWakeDelayNs before invoking FUTEX_WAKE to reduce
// the probability that the wakeup comes before the wait, preventing the wait
// from ever taking effect and causing the benchmark to underestimate the
// actual wakeup time.
constexpr int64_t kBeforeWakeDelayNs = 500;
std::atomic<int32_t> v(0);
ScopedThread t([&] {
for (int i = 0; i < state.max_iterations; i++) {
SpinNanos(delay_ns);
while (v.load(std::memory_order_acquire) == 0) {
FutexWait(&v, 0);
}
SpinNanos(kBeforeWakeDelayNs + delay_ns);
v.store(0, std::memory_order_release);
FutexWake(&v, 1);
}
});
for (auto _ : state) {
SpinNanos(kBeforeWakeDelayNs + delay_ns);
v.store(1, std::memory_order_release);
FutexWake(&v, 1);
SpinNanos(delay_ns);
while (v.load(std::memory_order_acquire) == 1) {
FutexWait(&v, 1);
}
}
}
BENCHMARK(BM_FutexRoundtripDelayed)
->MinTime(5)
->UseRealTime()
->Arg(0)
->Arg(10)
->Arg(20)
->Arg(50)
->Arg(100);
} // namespace
} // namespace testing
} // namespace gvisor
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