3b246fa863
Usleep(100) in runqgrab negatively affects latency and throughput of parallel application. We are sleeping instead of doing useful work. This is effect is particularly visible on windows where minimal sleep duration is 1-15ms. Reduce sleep from 100us to 3us and use osyield on windows. Sync chan send/recv takes ~50ns, so 3us gives us ~50x overshoot. benchmark old ns/op new ns/op delta BenchmarkChanSync-12 216 217 +0.46% BenchmarkChanSyncWork-12 27213 25816 -5.13% CPU consumption goes up from 106% to 108% in the first case, and from 107% to 125% in the second case. Test case from #14790 on windows: BenchmarkDefaultResolution-8 4583372 29720 -99.35% Benchmark1ms-8 992056 30701 -96.91% 99-th latency percentile for HTTP request serving is improved by up to 15% (see http://golang.org/cl/20835 for details). The following benchmarks are from the change that originally added this sleep (see https://golang.org/s/go15gomaxprocs): name old time/op new time/op delta Chain 22.6µs ± 2% 22.7µs ± 6% ~ (p=0.905 n=9+10) ChainBuf 22.4µs ± 3% 22.5µs ± 4% ~ (p=0.780 n=9+10) Chain-2 23.5µs ± 4% 24.9µs ± 1% +5.66% (p=0.000 n=10+9) ChainBuf-2 23.7µs ± 1% 24.4µs ± 1% +3.31% (p=0.000 n=9+10) Chain-4 24.2µs ± 2% 25.1µs ± 3% +3.70% (p=0.000 n=9+10) ChainBuf-4 24.4µs ± 5% 25.0µs ± 2% +2.37% (p=0.023 n=10+10) Powser 2.37s ± 1% 2.37s ± 1% ~ (p=0.423 n=8+9) Powser-2 2.48s ± 2% 2.57s ± 2% +3.74% (p=0.000 n=10+9) Powser-4 2.66s ± 1% 2.75s ± 1% +3.40% (p=0.000 n=10+10) Sieve 13.3s ± 2% 13.3s ± 2% ~ (p=1.000 n=10+9) Sieve-2 7.00s ± 2% 7.44s ±16% ~ (p=0.408 n=8+10) Sieve-4 4.13s ±21% 3.85s ±22% ~ (p=0.113 n=9+9) Fixes #14790 Change-Id: Ie7c6a1c4f9c8eb2f5d65ab127a3845386d6f8b5d Reviewed-on: https://go-review.googlesource.com/20835 Reviewed-by: Austin Clements <austin@google.com> |
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