• Austin Clements's avatar
    runtime: make stack re-scan O(# dirty stacks) · 2a889b9d
    Austin Clements authored
    Currently the stack re-scan during mark termination is O(# stacks)
    because we enqueue a root marking job for every goroutine. It takes
    ~34ns to process this root marking job for a valid (clean) stack, so
    at around 300k goroutines we exceed the 10ms pause goal. A non-trivial
    portion of this time is spent simply taking the cache miss to check
    the gcscanvalid flag, so simply optimizing the path that handles clean
    stacks can only improve this so much.
    
    Fix this by keeping an explicit list of goroutines with dirty stacks
    that need to be rescanned. When a goroutine first transitions to
    running after a stack scan and marks its stack dirty, it adds itself
    to this list. We enqueue root marking jobs only for the goroutines in
    this list, so this improves stack re-scanning asymptotically by
    completely eliminating time spent on clean goroutines.
    
    This reduces mark termination time for 500k idle goroutines from 15ms
    to 238µs. Overall performance effect is negligible.
    
    name \ 95%ile-time/markTerm     old           new         delta
    IdleGs/gs:500000/gomaxprocs:12  15000µs ± 0%  238µs ± 5%  -98.41% (p=0.000 n=10+10)
    
    name              old time/op  new time/op  delta
    XBenchGarbage-12  2.30ms ± 3%  2.29ms ± 1%  -0.43%  (p=0.049 n=17+18)
    
    name                      old time/op    new time/op    delta
    BinaryTree17-12              2.57s ± 3%     2.59s ± 2%    ~     (p=0.141 n=19+20)
    Fannkuch11-12                2.09s ± 0%     2.10s ± 1%  +0.53%  (p=0.000 n=19+19)
    FmtFprintfEmpty-12          45.3ns ± 3%    45.2ns ± 2%    ~     (p=0.845 n=20+20)
    FmtFprintfString-12          129ns ± 0%     127ns ± 0%  -1.55%  (p=0.000 n=16+16)
    FmtFprintfInt-12             123ns ± 0%     119ns ± 1%  -3.24%  (p=0.000 n=19+19)
    FmtFprintfIntInt-12          195ns ± 1%     189ns ± 1%  -3.11%  (p=0.000 n=17+17)
    FmtFprintfPrefixedInt-12     193ns ± 1%     187ns ± 1%  -3.06%  (p=0.000 n=19+19)
    FmtFprintfFloat-12           254ns ± 0%     255ns ± 1%  +0.35%  (p=0.001 n=14+17)
    FmtManyArgs-12               781ns ± 0%     770ns ± 0%  -1.48%  (p=0.000 n=16+19)
    GobDecode-12                7.00ms ± 1%    6.98ms ± 1%    ~     (p=0.563 n=19+19)
    GobEncode-12                5.91ms ± 1%    5.92ms ± 0%    ~     (p=0.118 n=19+18)
    Gzip-12                      219ms ± 1%     215ms ± 1%  -1.81%  (p=0.000 n=18+18)
    Gunzip-12                   37.2ms ± 0%    37.4ms ± 0%  +0.45%  (p=0.000 n=17+19)
    HTTPClientServer-12         76.9µs ± 3%    77.5µs ± 2%  +0.81%  (p=0.030 n=20+19)
    JSONEncode-12               15.0ms ± 0%    14.8ms ± 1%  -0.88%  (p=0.001 n=15+19)
    JSONDecode-12               50.6ms ± 0%    53.2ms ± 2%  +5.07%  (p=0.000 n=17+19)
    Mandelbrot200-12            4.05ms ± 0%    4.05ms ± 1%    ~     (p=0.581 n=16+17)
    GoParse-12                  3.34ms ± 1%    3.30ms ± 1%  -1.21%  (p=0.000 n=15+20)
    RegexpMatchEasy0_32-12      69.6ns ± 1%    69.8ns ± 2%    ~     (p=0.566 n=19+19)
    RegexpMatchEasy0_1K-12       238ns ± 1%     236ns ± 0%  -0.91%  (p=0.000 n=17+13)
    RegexpMatchEasy1_32-12      69.8ns ± 1%    70.0ns ± 1%  +0.23%  (p=0.026 n=17+16)
    RegexpMatchEasy1_1K-12       371ns ± 1%     363ns ± 1%  -2.07%  (p=0.000 n=19+19)
    RegexpMatchMedium_32-12      107ns ± 2%     106ns ± 1%  -0.51%  (p=0.031 n=18+20)
    RegexpMatchMedium_1K-12     33.0µs ± 0%    32.9µs ± 0%  -0.30%  (p=0.004 n=16+16)
    RegexpMatchHard_32-12       1.70µs ± 0%    1.70µs ± 0%  +0.45%  (p=0.000 n=16+17)
    RegexpMatchHard_1K-12       51.1µs ± 2%    51.4µs ± 1%  +0.53%  (p=0.000 n=17+19)
    Revcomp-12                   378ms ± 1%     385ms ± 1%  +1.92%  (p=0.000 n=19+18)
    Template-12                 64.3ms ± 2%    65.0ms ± 2%  +1.09%  (p=0.001 n=19+19)
    TimeParse-12                 315ns ± 1%     317ns ± 2%    ~     (p=0.108 n=18+20)
    TimeFormat-12                360ns ± 1%     337ns ± 0%  -6.30%  (p=0.000 n=18+13)
    [Geo mean]                  51.8µs         51.6µs       -0.48%
    
    Change-Id: Icf8994671476840e3998236e15407a505d4c760c
    Reviewed-on: https://go-review.googlesource.com/20700Reviewed-by: 's avatarRick Hudson <rlh@golang.org>
    Run-TryBot: Austin Clements <austin@google.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    2a889b9d
mgc.go 63.2 KB