990124da2a
CL 36792 fixed #17953, a linear scan caused by n goroutines piling into two different locks that hashed to the same bucket in the semaphore table. In that CL, n goroutines contending for 2 unfortunately chosen locks went from O(n²) to O(n). This CL fixes a different linear scan, when n goroutines are contending for n/2 different locks that all hash to the same bucket in the semaphore table. In this CL, n goroutines contending for n/2 unfortunately chosen locks goes from O(n²) to O(n log n). This case is much less likely, but any linear scan eventually hurts, so we might as well fix it while the problem is fresh in our minds. The new test in this CL checks for both linear scans. The effect of this CL on the sync benchmarks is negligible (but it fixes the new test). name old time/op new time/op delta Cond1-48 576ns ±10% 575ns ±13% ~ (p=0.679 n=71+71) Cond2-48 1.59µs ± 8% 1.61µs ± 9% ~ (p=0.107 n=73+69) Cond4-48 4.56µs ± 7% 4.55µs ± 7% ~ (p=0.670 n=74+72) Cond8-48 9.87µs ± 9% 9.90µs ± 7% ~ (p=0.507 n=69+73) Cond16-48 20.4µs ± 7% 20.4µs ±10% ~ (p=0.588 n=69+71) Cond32-48 45.4µs ±10% 45.4µs ±14% ~ (p=0.944 n=73+73) UncontendedSemaphore-48 19.7ns ±12% 19.7ns ± 8% ~ (p=0.589 n=65+63) ContendedSemaphore-48 55.4ns ±26% 54.9ns ±32% ~ (p=0.441 n=75+75) MutexUncontended-48 0.63ns ± 0% 0.63ns ± 0% ~ (all equal) Mutex-48 210ns ± 6% 213ns ±10% +1.30% (p=0.035 n=70+74) MutexSlack-48 210ns ± 7% 211ns ± 9% ~ (p=0.184 n=71+72) MutexWork-48 299ns ± 5% 300ns ± 5% ~ (p=0.678 n=73+75) MutexWorkSlack-48 302ns ± 6% 300ns ± 5% ~ (p=0.149 n=74+72) MutexNoSpin-48 135ns ± 6% 135ns ±10% ~ (p=0.788 n=67+75) MutexSpin-48 693ns ± 5% 689ns ± 6% ~ (p=0.092 n=65+74) Once-48 0.22ns ±25% 0.22ns ±24% ~ (p=0.882 n=74+73) Pool-48 5.88ns ±36% 5.79ns ±24% ~ (p=0.655 n=69+69) PoolOverflow-48 4.79µs ±18% 4.87µs ±20% ~ (p=0.233 n=75+75) SemaUncontended-48 0.80ns ± 1% 0.82ns ± 8% +2.46% (p=0.000 n=60+74) SemaSyntNonblock-48 103ns ± 4% 102ns ± 5% -1.11% (p=0.003 n=75+75) SemaSyntBlock-48 104ns ± 4% 104ns ± 5% ~ (p=0.231 n=71+75) SemaWorkNonblock-48 128ns ± 4% 129ns ± 6% +1.51% (p=0.000 n=63+75) SemaWorkBlock-48 129ns ± 8% 130ns ± 7% ~ (p=0.072 n=75+74) RWMutexUncontended-48 2.35ns ± 1% 2.35ns ± 0% ~ (p=0.144 n=70+55) RWMutexWrite100-48 139ns ±18% 141ns ±21% ~ (p=0.071 n=75+73) RWMutexWrite10-48 145ns ± 9% 145ns ± 8% ~ (p=0.553 n=75+75) RWMutexWorkWrite100-48 297ns ±13% 297ns ±15% ~ (p=0.519 n=75+74) RWMutexWorkWrite10-48 588ns ± 7% 585ns ± 5% ~ (p=0.173 n=73+70) WaitGroupUncontended-48 0.87ns ± 0% 0.87ns ± 0% ~ (all equal) WaitGroupAddDone-48 63.2ns ± 4% 62.7ns ± 4% -0.82% (p=0.027 n=72+75) WaitGroupAddDoneWork-48 109ns ± 5% 109ns ± 4% ~ (p=0.233 n=75+75) WaitGroupWait-48 0.17ns ± 0% 0.16ns ±16% -8.55% (p=0.000 n=56+75) WaitGroupWaitWork-48 1.78ns ± 1% 2.08ns ± 5% +16.92% (p=0.000 n=74+70) WaitGroupActuallyWait-48 52.0ns ± 3% 50.6ns ± 5% -2.70% (p=0.000 n=71+69) https://perf.golang.org/search?q=upload:20170215.1 Change-Id: Ia29a8bd006c089e401ec4297c3038cca656bcd0a Reviewed-on: https://go-review.googlesource.com/37103 Run-TryBot: Russ Cox <rsc@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> |
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