• Dmitry Vyukov's avatar
    sync: make Mutex more fair · 0556e262
    Dmitry Vyukov authored
    Add new starvation mode for Mutex.
    In starvation mode ownership is directly handed off from
    unlocking goroutine to the next waiter. New arriving goroutines
    don't compete for ownership.
    Unfair wait time is now limited to 1ms.
    Also fix a long standing bug that goroutines were requeued
    at the tail of the wait queue. That lead to even more unfair
    acquisition times with multiple waiters.
    
    Performance of normal mode is not considerably affected.
    
    Fixes #13086
    
    On the provided in the issue lockskew program:
    
    done in 1.207853ms
    done in 1.177451ms
    done in 1.184168ms
    done in 1.198633ms
    done in 1.185797ms
    done in 1.182502ms
    done in 1.316485ms
    done in 1.211611ms
    done in 1.182418ms
    
    name                    old time/op  new time/op   delta
    MutexUncontended-48     0.65ns ± 0%   0.65ns ± 1%     ~           (p=0.087 n=10+10)
    Mutex-48                 112ns ± 1%    114ns ± 1%   +1.69%        (p=0.000 n=10+10)
    MutexSlack-48            113ns ± 0%     87ns ± 1%  -22.65%         (p=0.000 n=8+10)
    MutexWork-48             149ns ± 0%    145ns ± 0%   -2.48%         (p=0.000 n=9+10)
    MutexWorkSlack-48        149ns ± 0%    122ns ± 3%  -18.26%         (p=0.000 n=6+10)
    MutexNoSpin-48           103ns ± 4%    105ns ± 3%     ~           (p=0.089 n=10+10)
    MutexSpin-48             490ns ± 4%    515ns ± 6%   +5.08%        (p=0.006 n=10+10)
    Cond32-48               13.4µs ± 6%   13.1µs ± 5%   -2.75%        (p=0.023 n=10+10)
    RWMutexWrite100-48      53.2ns ± 3%   41.2ns ± 3%  -22.57%        (p=0.000 n=10+10)
    RWMutexWrite10-48       45.9ns ± 2%   43.9ns ± 2%   -4.38%        (p=0.000 n=10+10)
    RWMutexWorkWrite100-48   122ns ± 2%    134ns ± 1%   +9.92%        (p=0.000 n=10+10)
    RWMutexWorkWrite10-48    206ns ± 1%    188ns ± 1%   -8.52%         (p=0.000 n=8+10)
    Cond32-24               12.1µs ± 3%   12.4µs ± 3%   +1.98%         (p=0.043 n=10+9)
    MutexUncontended-24     0.74ns ± 1%   0.75ns ± 1%     ~           (p=0.650 n=10+10)
    Mutex-24                 122ns ± 2%    124ns ± 1%   +1.31%        (p=0.007 n=10+10)
    MutexSlack-24           96.9ns ± 2%  102.8ns ± 2%   +6.11%        (p=0.000 n=10+10)
    MutexWork-24             146ns ± 1%    135ns ± 2%   -7.70%         (p=0.000 n=10+9)
    MutexWorkSlack-24        135ns ± 1%    128ns ± 2%   -5.01%         (p=0.000 n=10+9)
    MutexNoSpin-24           114ns ± 3%    110ns ± 4%   -3.84%        (p=0.000 n=10+10)
    MutexSpin-24             482ns ± 4%    475ns ± 8%     ~           (p=0.286 n=10+10)
    RWMutexWrite100-24      43.0ns ± 3%   43.1ns ± 2%     ~           (p=0.956 n=10+10)
    RWMutexWrite10-24       43.4ns ± 1%   43.2ns ± 1%     ~            (p=0.085 n=10+9)
    RWMutexWorkWrite100-24   130ns ± 3%    131ns ± 3%     ~           (p=0.747 n=10+10)
    RWMutexWorkWrite10-24    191ns ± 1%    192ns ± 1%     ~           (p=0.210 n=10+10)
    Cond32-12               11.5µs ± 2%   11.7µs ± 2%   +1.98%        (p=0.002 n=10+10)
    MutexUncontended-12     1.48ns ± 0%   1.50ns ± 1%   +1.08%        (p=0.004 n=10+10)
    Mutex-12                 141ns ± 1%    143ns ± 1%   +1.63%        (p=0.000 n=10+10)
    MutexSlack-12            121ns ± 0%    119ns ± 0%   -1.65%          (p=0.001 n=8+9)
    MutexWork-12             141ns ± 2%    150ns ± 3%   +6.36%         (p=0.000 n=9+10)
    MutexWorkSlack-12        131ns ± 0%    138ns ± 0%   +5.73%         (p=0.000 n=9+10)
    MutexNoSpin-12          87.0ns ± 1%   83.7ns ± 1%   -3.80%        (p=0.000 n=10+10)
    MutexSpin-12             364ns ± 1%    377ns ± 1%   +3.77%        (p=0.000 n=10+10)
    RWMutexWrite100-12      42.8ns ± 1%   43.9ns ± 1%   +2.41%         (p=0.000 n=8+10)
    RWMutexWrite10-12       39.8ns ± 4%   39.3ns ± 1%     ~            (p=0.433 n=10+9)
    RWMutexWorkWrite100-12   131ns ± 1%    131ns ± 0%     ~            (p=0.591 n=10+9)
    RWMutexWorkWrite10-12    173ns ± 1%    174ns ± 0%     ~            (p=0.059 n=10+8)
    Cond32-6                10.9µs ± 2%   10.9µs ± 2%     ~           (p=0.739 n=10+10)
    MutexUncontended-6      2.97ns ± 0%   2.97ns ± 0%     ~     (all samples are equal)
    Mutex-6                  122ns ± 6%    122ns ± 2%     ~           (p=0.668 n=10+10)
    MutexSlack-6             149ns ± 3%    142ns ± 3%   -4.63%        (p=0.000 n=10+10)
    MutexWork-6              136ns ± 3%    140ns ± 5%     ~           (p=0.077 n=10+10)
    MutexWorkSlack-6         152ns ± 0%    138ns ± 2%   -9.21%         (p=0.000 n=6+10)
    MutexNoSpin-6            150ns ± 1%    152ns ± 0%   +1.50%         (p=0.000 n=8+10)
    MutexSpin-6              726ns ± 0%    730ns ± 1%     ~           (p=0.069 n=10+10)
    RWMutexWrite100-6       40.6ns ± 1%   40.9ns ± 1%   +0.91%         (p=0.001 n=8+10)
    RWMutexWrite10-6        37.1ns ± 0%   37.0ns ± 1%     ~            (p=0.386 n=9+10)
    RWMutexWorkWrite100-6    133ns ± 1%    134ns ± 1%   +1.01%         (p=0.005 n=9+10)
    RWMutexWorkWrite10-6     152ns ± 0%    152ns ± 0%     ~     (all samples are equal)
    Cond32-2                7.86µs ± 2%   7.95µs ± 2%   +1.10%        (p=0.023 n=10+10)
    MutexUncontended-2      8.10ns ± 0%   9.11ns ± 4%  +12.44%         (p=0.000 n=9+10)
    Mutex-2                 32.9ns ± 9%   38.4ns ± 6%  +16.58%        (p=0.000 n=10+10)
    MutexSlack-2            93.4ns ± 1%   98.5ns ± 2%   +5.39%         (p=0.000 n=10+9)
    MutexWork-2             40.8ns ± 3%   43.8ns ± 7%   +7.38%         (p=0.000 n=10+9)
    MutexWorkSlack-2        98.6ns ± 5%  108.2ns ± 2%   +9.80%         (p=0.000 n=10+8)
    MutexNoSpin-2            399ns ± 1%    398ns ± 2%     ~             (p=0.463 n=8+9)
    MutexSpin-2             1.99µs ± 3%   1.97µs ± 1%   -0.81%          (p=0.003 n=9+8)
    RWMutexWrite100-2       37.6ns ± 5%   46.0ns ± 4%  +22.17%         (p=0.000 n=10+8)
    RWMutexWrite10-2        50.1ns ± 6%   36.8ns ±12%  -26.46%         (p=0.000 n=9+10)
    RWMutexWorkWrite100-2    136ns ± 0%    134ns ± 2%   -1.80%          (p=0.001 n=7+9)
    RWMutexWorkWrite10-2     140ns ± 1%    138ns ± 1%   -1.50%        (p=0.000 n=10+10)
    Cond32                  5.93µs ± 1%   5.91µs ± 0%     ~            (p=0.411 n=9+10)
    MutexUncontended        15.9ns ± 0%   15.8ns ± 0%   -0.63%          (p=0.000 n=8+8)
    Mutex                   15.9ns ± 0%   15.8ns ± 0%   -0.44%        (p=0.003 n=10+10)
    MutexSlack              26.9ns ± 3%   26.7ns ± 2%     ~           (p=0.084 n=10+10)
    MutexWork               47.8ns ± 0%   47.9ns ± 0%   +0.21%          (p=0.014 n=9+8)
    MutexWorkSlack          54.9ns ± 3%   54.5ns ± 3%     ~           (p=0.254 n=10+10)
    MutexNoSpin              786ns ± 2%    765ns ± 1%   -2.66%        (p=0.000 n=10+10)
    MutexSpin               3.87µs ± 1%   3.83µs ± 0%   -0.85%          (p=0.005 n=9+8)
    RWMutexWrite100         21.2ns ± 2%   21.0ns ± 1%   -0.88%         (p=0.018 n=10+9)
    RWMutexWrite10          22.6ns ± 1%   22.6ns ± 0%     ~             (p=0.471 n=9+9)
    RWMutexWorkWrite100      132ns ± 0%    132ns ± 0%     ~     (all samples are equal)
    RWMutexWorkWrite10       124ns ± 0%    123ns ± 0%     ~           (p=0.656 n=10+10)
    
    Change-Id: I66412a3a0980df1233ad7a5a0cd9723b4274528b
    Reviewed-on: https://go-review.googlesource.com/34310
    Run-TryBot: Russ Cox <rsc@golang.org>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarRuss Cox <rsc@golang.org>
    0556e262
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