1 files changed, 248 insertions, 0 deletions
diff --git a/test/perf/linux/futex_benchmark.cc b/test/perf/linux/futex_benchmark.cc
new file mode 100644
index 000000000..b349d50bf
--- /dev/null
+++ b/test/perf/linux/futex_benchmark.cc
@@ -0,0 +1,248 @@
+// 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_BITSET_MATCH_ANY, nullptr);
+}
+
+inline int FutexWaitRelativeTimeout(std::atomic<int32_t>* v, int32_t val,
+                                    const struct timespec* reltime) {
+  return syscall(SYS_futex, v, FUTEX_WAIT_PRIVATE, reltime);
+}
+
+inline int FutexWaitAbsoluteTimeout(std::atomic<int32_t>* v, int32_t val,
+                                    const struct timespec* abstime) {
+  return syscall(SYS_futex, v, FUTEX_BITSET_MATCH_ANY, abstime);
+}
+
+inline int FutexWaitBitsetAbsoluteTimeout(std::atomic<int32_t>* v, int32_t val,
+                                          int32_t bits,
+                                          const struct timespec* abstime) {
+  return syscall(SYS_futex, v, FUTEX_WAIT_BITSET_PRIVATE | FUTEX_CLOCK_REALTIME,
+                 val, abstime, nullptr, bits);
+}
+
+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) {
+    EXPECT_EQ(0, FutexWake(&v, 1));
+  }
+}
+
+BENCHMARK(BM_FutexWakeNop);
+
+// 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) {
+    EXPECT_EQ(-EAGAIN, FutexWait(&v, 1));
+  }
+}
+
+BENCHMARK(BM_FutexWaitNop);
+
+// 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_FutexWaitTimeout(benchmark::State& state) {
+  const int timeout_ns = state.range(0);
+  std::atomic<int32_t> v(0);
+  auto ts = absl::ToTimespec(absl::Nanoseconds(timeout_ns));
+
+  for (auto _ : state) {
+    EXPECT_EQ(-ETIMEDOUT, FutexWaitRelativeTimeout(&v, 0, &ts));
+  }
+}
+
+BENCHMARK(BM_FutexWaitTimeout)
+    ->Arg(1)
+    ->Arg(10)
+    ->Arg(100)
+    ->Arg(1000)
+    ->Arg(10000);
+
+// This calls FUTEX_WAIT_BITSET with CLOCK_REALTIME.
+void BM_FutexWaitBitset(benchmark::State& state) {
+  std::atomic<int32_t> v(0);
+  int timeout_ns = state.range(0);
+  auto ts = absl::ToTimespec(absl::Nanoseconds(timeout_ns));
+  for (auto _ : state) {
+    EXPECT_EQ(-ETIMEDOUT, FutexWaitBitsetAbsoluteTimeout(&v, 0, 1, &ts));
+  }
+}
+
+BENCHMARK(BM_FutexWaitBitset)->Range(0, 100000);
+
+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)
+    ->Arg(0)
+    ->Arg(10)
+    ->Arg(20)
+    ->Arg(50)
+    ->Arg(100);
+
+// FutexLock is a simple, dumb futex based lock implementation.
+// It will try to acquire the lock by atomically incrementing the
+// lock word. If it did not increment the lock from 0 to 1, someone
+// else has the lock, so it will FUTEX_WAIT until it is woken in
+// the unlock path.
+class FutexLock {
+ public:
+  FutexLock() : lock_word_(0) {}
+
+  void lock(struct timespec* deadline) {
+    int32_t val;
+    while ((val = lock_word_.fetch_add(1, std::memory_order_acquire) + 1) !=
+           1) {
+      // If we didn't get the lock by incrementing from 0 to 1,
+      // do a FUTEX_WAIT with the desired current value set to
+      // val. If val is no longer what the atomic increment returned,
+      // someone might have set it to 0 so we can try to acquire
+      // again.
+      int ret = FutexWaitAbsoluteTimeout(&lock_word_, val, deadline);
+      if (ret == 0 || ret == -EWOULDBLOCK || ret == -EINTR) {
+        continue;
+      } else {
+        FAIL() << "unexpected FUTEX_WAIT return: " << ret;
+      }
+    }
+  }
+
+  void unlock() {
+    // Store 0 into the lock word and wake one waiter. We intentionally
+    // ignore the return value of the FUTEX_WAKE here, since there may be
+    // no waiters to wake anyway.
+    lock_word_.store(0, std::memory_order_release);
+    (void)FutexWake(&lock_word_, 1);
+  }
+
+ private:
+  std::atomic<int32_t> lock_word_;
+};
+
+FutexLock* test_lock;  // Used below.
+
+void FutexContend(benchmark::State& state, int thread_index,
+                  struct timespec* deadline) {
+  int counter = 0;
+  if (thread_index == 0) {
+    test_lock = new FutexLock();
+  }
+  for (auto _ : state) {
+    test_lock->lock(deadline);
+    counter++;
+    test_lock->unlock();
+  }
+  if (thread_index == 0) {
+    delete test_lock;
+  }
+  state.SetItemsProcessed(state.iterations());
+}
+
+void BM_FutexContend(benchmark::State& state) {
+  FutexContend(state, state.thread_index, nullptr);
+}
+
+BENCHMARK(BM_FutexContend)->ThreadRange(1, 1024)->UseRealTime();
+
+void BM_FutexDeadlineContend(benchmark::State& state) {
+  auto deadline = absl::ToTimespec(absl::Now() + absl::Minutes(10));
+  FutexContend(state, state.thread_index, &deadline);
+}
+
+BENCHMARK(BM_FutexDeadlineContend)->ThreadRange(1, 1024)->UseRealTime();
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor