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Commit 30b22b4a authored by Dave Watson's avatar Dave Watson Committed by Facebook Github Bot
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Only wake a single waker, instead of all waiters 

Summary: Only wake a single waiter.

Reviewed By: davidtgoldblatt

Differential Revision: D6595881

fbshipit-source-id: 9393618bb619cb22b75ca91b27291b784fc5097c
parent b4d8c0a7
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Showing with 43 additions and 42 deletions
folly/MicroLock.cpp
View file @ 30b22b4a
......@@ -29,6 +29,7 @@ void MicroLockCore::lockSlowPath(uint32_t oldWord,
uint32_t newWord;
unsigned spins = 0;
uint32_t slotWaitBit = slotHeldBit << 1;
uint32_t needWaitBit = 0;
retry:
if ((oldWord & slotHeldBit) != 0) {
......@@ -47,6 +48,7 @@ retry:
}
}
(void)wordPtr->futexWait(newWord, slotHeldBit);
needWaitBit = slotWaitBit;
} else if (spins > maxSpins) {
// sched_yield(), but more portable
std::this_thread::yield();
......@@ -57,7 +59,7 @@ retry:
goto retry;
}
newWord = oldWord | slotHeldBit;
newWord = oldWord | slotHeldBit | needWaitBit;
if (!wordPtr->compare_exchange_weak(oldWord,
newWord,
std::memory_order_acquire,
......
folly/MicroLock.h
View file @ 30b22b4a
......@@ -157,8 +157,7 @@ void MicroLockCore::unlock(unsigned slot) {
oldWord, newWord, std::memory_order_release, std::memory_order_relaxed));
if (oldWord & waitBit(slot)) {
// We don't track the number of waiters, so wake everyone
(void)wordPtr->futexWake(std::numeric_limits<int>::max(), heldBit(slot));
(void)wordPtr->futexWake(1, heldBit(slot));
}
}
......
folly/synchronization/test/SmallLocksBenchmark.cpp
View file @ 30b22b4a
......@@ -369,60 +369,60 @@ locks_benchmark --bm_min_iters=100000
56-core Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
std::mutex:
Sum: 3674921 Mean: 65623 stddev: 543
Lock time stats in us: mean 15 stddev 1169 max 10375
Sum: 3768590 Mean: 67296 stddev: 1318
Lock time stats in us: mean 15 stddev 1140 max 8002
InitLock<folly::MicroSpinLock>:
Sum: 3493610 Mean: 62385 stddev: 21015
Lock time stats in us: mean 31 stddev 1229 max 208816
Sum: 3548900 Mean: 63373 stddev: 31657
Lock time stats in us: mean 30 stddev 1210 max 287010
InitLock<folly::PicoSpinLock<uint16_t>>:
Sum: 2135792 Mean: 38139 stddev: 43269
Lock time stats in us: mean 50 stddev 2010 max 357286
Sum: 1051996 Mean: 18785 stddev: 3026
Lock time stats in us: mean 104 stddev 4082 max 376820
folly::MicroLock:
Sum: 1823152 Mean: 32556 stddev: 10299
Lock time stats in us: mean 49 stddev 2355 max 36064
Sum: 1871779 Mean: 33424 stddev: 10311
Lock time stats in us: mean 47 stddev 2294 max 20486
============================================================================
folly/synchronization/test/SmallLocksBenchmark.cpprelative time/iter iters/s
============================================================================
StdMutexUncontendedBenchmark 16.72ns 59.79M
MicroSpinLockUncontendedBenchmark 10.04ns 99.65M
StdMutexUncontendedBenchmark 16.73ns 59.78M
MicroSpinLockUncontendedBenchmark 10.03ns 99.67M
PicoSpinLockUncontendedBenchmark 11.25ns 88.90M
MicroLockUncontendedBenchmark 21.59ns 46.31M
MicroLockUncontendedBenchmark 21.59ns 46.32M
VirtualFunctionCall 76.02ps 13.15G
----------------------------------------------------------------------------
----------------------------------------------------------------------------
std_mutex(1thread) 717.69ns 1.39M
folly_microspin(1thread) 117.51% 610.77ns 1.64M
folly_picospin(1thread) 116.31% 617.07ns 1.62M
folly_microlock(1thread) 116.12% 618.07ns 1.62M
std_mutex(1thread) 655.60ns 1.53M
folly_microspin(1thread) 96.79% 677.31ns 1.48M
folly_picospin(1thread) 118.13% 554.96ns 1.80M
folly_microlock(1thread) 100.04% 655.31ns 1.53M
----------------------------------------------------------------------------
std_mutex(2thread) 1.23us 813.13K
folly_microspin(2thread) 165.99% 740.92ns 1.35M
folly_picospin(2thread) 143.34% 857.99ns 1.17M
folly_microlock(2thread) 133.62% 920.40ns 1.09M
std_mutex(2thread) 1.22us 816.56K
folly_microspin(2thread) 146.21% 837.59ns 1.19M
folly_picospin(2thread) 168.33% 727.51ns 1.37M
folly_microlock(2thread) 136.43% 897.65ns 1.11M
----------------------------------------------------------------------------
std_mutex(4thread) 2.58us 387.69K
folly_microspin(4thread) 121.91% 2.12us 472.62K
folly_picospin(4thread) 132.37% 1.95us 513.19K
folly_microlock(4thread) 104.59% 2.47us 405.49K
std_mutex(4thread) 2.56us 390.99K
folly_microspin(4thread) 128.05% 2.00us 500.67K
folly_picospin(4thread) 117.95% 2.17us 461.18K
folly_microlock(4thread) 101.01% 2.53us 394.94K
----------------------------------------------------------------------------
std_mutex(8thread) 5.92us 169.00K
folly_microspin(8thread) 141.90% 4.17us 239.81K
folly_picospin(8thread) 89.49% 6.61us 151.24K
folly_microlock(8thread) 84.45% 7.01us 142.71K
std_mutex(8thread) 5.59us 179.01K
folly_microspin(8thread) 119.13% 4.69us 213.26K
folly_picospin(8thread) 82.00% 6.81us 146.79K
folly_microlock(8thread) 84.50% 6.61us 151.26K
----------------------------------------------------------------------------
std_mutex(16thread) 11.60us 86.20K
folly_microspin(16thread) 99.89% 11.61us 86.10K
folly_picospin(16thread) 62.22% 18.64us 53.63K
folly_microlock(16thread) 63.53% 18.26us 54.76K
std_mutex(16thread) 11.52us 86.80K
folly_microspin(16thread) 98.18% 11.73us 85.22K
folly_picospin(16thread) 61.18% 18.83us 53.10K
folly_microlock(16thread) 51.93% 22.19us 45.07K
----------------------------------------------------------------------------
std_mutex(32thread) 33.43us 29.91K
folly_microspin(32thread) 108.98% 30.67us 32.60K
folly_picospin(32thread) 33.06% 101.11us 9.89K
folly_microlock(32thread) 55.95% 59.75us 16.74K
std_mutex(32thread) 31.91us 31.34K
folly_microspin(32thread) 101.74% 31.37us 31.88K
folly_picospin(32thread) 32.43% 98.39us 10.16K
folly_microlock(32thread) 56.35% 56.63us 17.66K
----------------------------------------------------------------------------
std_mutex(64thread) 36.79us 27.18K
folly_microspin(64thread) 106.69% 34.48us 29.00K
folly_picospin(64thread) 35.82% 102.72us 9.74K
folly_microlock(64thread) 57.42% 64.08us 15.61K
std_mutex(64thread) 36.77us 27.20K
folly_microspin(64thread) 102.25% 35.96us 27.81K
folly_picospin(64thread) 32.30% 113.83us 8.78K
folly_microlock(64thread) 55.54% 66.21us 15.10K
============================================================================
*/
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