![]() 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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