diff options
| -rw-r--r-- | absl/synchronization/mutex.cc | 34 |
1 files changed, 26 insertions, 8 deletions
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc index 69103ed8..b0f412bf 100644 --- a/absl/synchronization/mutex.cc +++ b/absl/synchronization/mutex.cc @@ -135,25 +135,42 @@ enum DelayMode { AGGRESSIVE, GENTLE }; struct ABSL_CACHELINE_ALIGNED MutexGlobals { absl::once_flag once; int spinloop_iterations = 0; - int32_t mutex_sleep_limit[2] = {}; + int32_t mutex_sleep_spins[2] = {}; + absl::Duration mutex_sleep_time; }; +absl::Duration MeasureTimeToYield() { + absl::Time before = absl::Now(); + ABSL_INTERNAL_C_SYMBOL(AbslInternalMutexYield)(); + return absl::Now() - before; +} + const MutexGlobals &GetMutexGlobals() { ABSL_CONST_INIT static MutexGlobals data; absl::base_internal::LowLevelCallOnce(&data.once, [&]() { const int num_cpus = absl::base_internal::NumCPUs(); data.spinloop_iterations = num_cpus > 1 ? 1500 : 0; - // If this a uniprocessor, only yield/sleep. Otherwise, if the mode is + // If this a uniprocessor, only yield/sleep. + // Real-time threads are often unable to yield, so the sleep time needs + // to be long enough to keep the calling thread asleep until scheduling + // happens. + // If this is multiprocessor, allow spinning. If the mode is // aggressive then spin many times before yielding. If the mode is // gentle then spin only a few times before yielding. Aggressive spinning // is used to ensure that an Unlock() call, which must get the spin lock // for any thread to make progress gets it without undue delay. if (num_cpus > 1) { - data.mutex_sleep_limit[AGGRESSIVE] = 5000; - data.mutex_sleep_limit[GENTLE] = 250; + data.mutex_sleep_spins[AGGRESSIVE] = 5000; + data.mutex_sleep_spins[GENTLE] = 250; + data.mutex_sleep_time = absl::Microseconds(10); } else { - data.mutex_sleep_limit[AGGRESSIVE] = 0; - data.mutex_sleep_limit[GENTLE] = 0; + data.mutex_sleep_spins[AGGRESSIVE] = 0; + data.mutex_sleep_spins[GENTLE] = 0; + data.mutex_sleep_time = MeasureTimeToYield() * 5; + data.mutex_sleep_time = + std::min(data.mutex_sleep_time, absl::Milliseconds(1)); + data.mutex_sleep_time = + std::max(data.mutex_sleep_time, absl::Microseconds(10)); } }); return data; @@ -164,7 +181,8 @@ namespace synchronization_internal { // Returns the Mutex delay on iteration `c` depending on the given `mode`. // The returned value should be used as `c` for the next call to `MutexDelay`. int MutexDelay(int32_t c, int mode) { - const int32_t limit = GetMutexGlobals().mutex_sleep_limit[mode]; + const int32_t limit = GetMutexGlobals().mutex_sleep_spins[mode]; + const absl::Duration sleep_time = GetMutexGlobals().mutex_sleep_time; if (c < limit) { // Spin. c++; @@ -177,7 +195,7 @@ int MutexDelay(int32_t c, int mode) { c++; } else { // Then wait. - absl::SleepFor(absl::Microseconds(10)); + absl::SleepFor(sleep_time); c = 0; } ABSL_TSAN_MUTEX_POST_DIVERT(nullptr, 0); |