868c8b374d
The sleep in question does not make sense if the stolen-from P cannot run the stolen G. The usleep(3) has been observed delaying execution of woken G's by ~60us; skipping it reduces the wakeup-to-execution latency to ~7us in these cases, improving CPU utilization. Benchmarks added by this change: name old time/op new time/op delta WakeupParallelSpinning/0s-12 14.4µs ± 1% 14.3µs ± 1% ~ (p=0.227 n=19+20) WakeupParallelSpinning/1µs-12 18.3µs ± 0% 18.3µs ± 1% ~ (p=0.950 n=20+19) WakeupParallelSpinning/2µs-12 22.3µs ± 1% 22.3µs ± 1% ~ (p=0.670 n=20+18) WakeupParallelSpinning/5µs-12 31.7µs ± 0% 31.7µs ± 0% ~ (p=0.460 n=20+17) WakeupParallelSpinning/10µs-12 51.8µs ± 0% 51.8µs ± 0% ~ (p=0.883 n=20+20) WakeupParallelSpinning/20µs-12 91.9µs ± 0% 91.9µs ± 0% ~ (p=0.245 n=20+20) WakeupParallelSpinning/50µs-12 214µs ± 0% 214µs ± 0% ~ (p=0.509 n=19+20) WakeupParallelSpinning/100µs-12 335µs ± 0% 335µs ± 0% -0.05% (p=0.006 n=17+15) WakeupParallelSyscall/0s-12 228µs ± 2% 129µs ± 1% -43.32% (p=0.000 n=20+19) WakeupParallelSyscall/1µs-12 232µs ± 1% 131µs ± 1% -43.60% (p=0.000 n=19+20) WakeupParallelSyscall/2µs-12 236µs ± 1% 133µs ± 1% -43.44% (p=0.000 n=18+19) WakeupParallelSyscall/5µs-12 248µs ± 2% 139µs ± 1% -43.68% (p=0.000 n=18+19) WakeupParallelSyscall/10µs-12 263µs ± 3% 150µs ± 2% -42.97% (p=0.000 n=18+20) WakeupParallelSyscall/20µs-12 281µs ± 2% 170µs ± 1% -39.43% (p=0.000 n=19+19) WakeupParallelSyscall/50µs-12 345µs ± 4% 246µs ± 7% -28.85% (p=0.000 n=20+20) WakeupParallelSyscall/100µs-12 460µs ± 5% 350µs ± 4% -23.85% (p=0.000 n=20+20) Benchmarks associated with the change that originally added this sleep (see https://golang.org/s/go15gomaxprocs): name old time/op new time/op delta Chain 19.4µs ± 2% 19.3µs ± 1% ~ (p=0.101 n=19+20) ChainBuf 19.5µs ± 2% 19.4µs ± 2% ~ (p=0.840 n=19+19) Chain-2 19.9µs ± 1% 19.9µs ± 2% ~ (p=0.734 n=19+19) ChainBuf-2 20.0µs ± 2% 20.0µs ± 2% ~ (p=0.175 n=19+17) Chain-4 20.3µs ± 1% 20.1µs ± 1% -0.62% (p=0.010 n=19+18) ChainBuf-4 20.3µs ± 1% 20.2µs ± 1% -0.52% (p=0.023 n=19+19) Powser 2.09s ± 1% 2.10s ± 3% ~ (p=0.908 n=19+19) Powser-2 2.21s ± 1% 2.20s ± 1% -0.35% (p=0.010 n=19+18) Powser-4 2.31s ± 2% 2.31s ± 2% ~ (p=0.578 n=18+19) Sieve 13.6s ± 1% 13.6s ± 1% ~ (p=0.909 n=17+18) Sieve-2 8.02s ±52% 7.28s ±15% ~ (p=0.336 n=20+16) Sieve-4 4.00s ±35% 3.98s ±26% ~ (p=0.654 n=20+18) Change-Id: I58edd8ce01075859d871e2348fc0833e9c01f70f Reviewed-on: https://go-review.googlesource.com/78538 Reviewed-by: Austin Clements <austin@google.com>
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