• Dmitry Vyukov's avatar
    runtime: sleep less when we can do work · 3b246fa8
    Dmitry Vyukov authored
    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/20835Reviewed-by: default avatarAustin Clements <austin@google.com>
    3b246fa8
chan_test.go 18.8 KB