runtime: decrease STW pause for goroutine profile

runtime: decrease STW pause for goroutine profile

The goroutine profile needs to stop the world to get a consistent
snapshot of all goroutines in the app. Leaving the world stopped while
iterating over allgs leads to a pause proportional to the number of
goroutines in the app (or its high-water mark).

Instead, do only a fixed amount of bookkeeping while the world is
stopped. Install a barrier so the scheduler confirms that a goroutine
appears in the profile, with its stack recorded exactly as it was during
the stop-the-world pause, before it allows that goroutine to execute.
Iterate over allgs while the app resumes normal operations, adding each
to the profile unless they've been scheduled in the meantime (and so
have profiled themselves). Stop the world a second time to remove the
barrier and do a fixed amount of cleanup work.

This increases both the fixed overhead and per-goroutine CPU-time cost
of GoroutineProfile. It also increases the wall-clock latency of the
call to GoroutineProfile, since the scheduler may interrupt it to
execute other goroutines.

    name                                  old time/op    new time/op    delta
    GoroutineProfile/small/loaded-8         1.05ms ± 5%    4.99ms ±31%   +376.85%  (p=0.000 n=10+9)
    GoroutineProfile/sparse/loaded-8        1.04ms ± 4%    3.61ms ±27%   +246.61%  (p=0.000 n=10+10)
    GoroutineProfile/large/loaded-8         7.69ms ±17%   20.35ms ± 4%   +164.50%  (p=0.000 n=10+10)
    GoroutineProfile/small/idle              958µs ± 0%    1820µs ±23%    +89.91%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/idle-8          1.00ms ± 3%    1.52ms ±17%    +51.18%  (p=0.000 n=10+10)
    GoroutineProfile/small/idle-8           1.01ms ± 4%    1.47ms ± 7%    +45.28%  (p=0.000 n=9+9)
    GoroutineProfile/sparse/idle             980µs ± 1%    1403µs ± 2%    +43.22%  (p=0.000 n=9+10)
    GoroutineProfile/large/idle-8           7.19ms ± 8%    8.43ms ±21%    +17.22%  (p=0.011 n=10+10)
    PingPongHog                              511ns ± 8%     585ns ± 9%    +14.39%  (p=0.000 n=10+10)
    GoroutineProfile/large/idle             6.71ms ± 0%    7.58ms ± 3%    +13.08%  (p=0.000 n=8+10)
    PingPongHog-8                            469ns ± 8%     509ns ±12%     +8.62%  (p=0.010 n=9+10)
    WakeupParallelSyscall/5µs                216µs ± 4%     229µs ± 3%     +6.06%  (p=0.000 n=10+9)
    WakeupParallelSyscall/5µs-8              147µs ± 1%     149µs ± 2%     +1.12%  (p=0.009 n=10+10)
    WakeupParallelSyscall/2µs-8              140µs ± 0%     142µs ± 1%     +1.11%  (p=0.001 n=10+9)
    WakeupParallelSyscall/50µs-8             236µs ± 0%     238µs ± 1%     +1.08%  (p=0.000 n=9+10)
    WakeupParallelSyscall/1µs-8              138µs ± 0%     140µs ± 1%     +1.05%  (p=0.013 n=10+9)
    Matmult                                 8.52ns ± 1%    8.61ns ± 0%     +0.98%  (p=0.002 n=10+8)
    WakeupParallelSyscall/10µs-8             157µs ± 1%     158µs ± 1%     +0.58%  (p=0.003 n=10+8)
    CreateGoroutinesSingle-8                 328ns ± 0%     330ns ± 1%     +0.57%  (p=0.000 n=9+9)
    WakeupParallelSpinning/100µs-8           343µs ± 0%     344µs ± 1%     +0.30%  (p=0.015 n=8+8)
    WakeupParallelSyscall/20µs-8             178µs ± 0%     178µs ± 0%     +0.18%  (p=0.043 n=10+9)
    StackGrowthDeep-8                       22.8µs ± 0%    22.9µs ± 0%     +0.12%  (p=0.006 n=10+10)
    StackGrowth                             1.06µs ± 0%    1.06µs ± 0%     +0.09%  (p=0.000 n=8+9)
    WakeupParallelSpinning/0s               10.7µs ± 0%    10.7µs ± 0%     +0.08%  (p=0.000 n=9+9)
    WakeupParallelSpinning/5µs              30.7µs ± 0%    30.7µs ± 0%     +0.04%  (p=0.000 n=10+10)
    WakeupParallelSpinning/100µs             411µs ± 0%     411µs ± 0%     +0.03%  (p=0.000 n=10+9)
    WakeupParallelSpinning/2µs              18.7µs ± 0%    18.7µs ± 0%     +0.02%  (p=0.026 n=10+10)
    WakeupParallelSpinning/20µs-8           93.0µs ± 0%    93.0µs ± 0%     +0.01%  (p=0.021 n=9+10)
    StackGrowth-8                            216ns ± 0%     216ns ± 0%       ~     (p=0.209 n=10+10)
    CreateGoroutinesParallel-8              49.5ns ± 2%    49.3ns ± 1%       ~     (p=0.591 n=10+10)
    CreateGoroutinesSingle                   699ns ±20%     748ns ±19%       ~     (p=0.353 n=10+10)
    WakeupParallelSpinning/0s-8             15.9µs ± 2%    16.0µs ± 3%       ~     (p=0.315 n=10+10)
    WakeupParallelSpinning/1µs              14.6µs ± 0%    14.6µs ± 0%       ~     (p=0.513 n=10+10)
    WakeupParallelSpinning/2µs-8            24.2µs ± 3%    24.1µs ± 2%       ~     (p=0.971 n=10+10)
    WakeupParallelSpinning/10µs             50.7µs ± 0%    50.7µs ± 0%       ~     (p=0.101 n=10+10)
    WakeupParallelSpinning/20µs             90.7µs ± 0%    90.7µs ± 0%       ~     (p=0.898 n=10+10)
    WakeupParallelSpinning/50µs              211µs ± 0%     211µs ± 0%       ~     (p=0.382 n=10+10)
    WakeupParallelSyscall/0s-8               137µs ± 1%     138µs ± 0%       ~     (p=0.075 n=10+10)
    WakeupParallelSyscall/1µs                216µs ± 1%     219µs ± 3%       ~     (p=0.065 n=10+9)
    WakeupParallelSyscall/2µs                214µs ± 7%     219µs ± 1%       ~     (p=0.101 n=10+8)
    WakeupParallelSyscall/50µs               317µs ± 5%     326µs ± 4%       ~     (p=0.123 n=10+10)
    WakeupParallelSyscall/100µs              450µs ± 9%     459µs ± 8%       ~     (p=0.247 n=10+10)
    WakeupParallelSyscall/100µs-8            337µs ± 0%     338µs ± 1%       ~     (p=0.089 n=10+10)
    WakeupParallelSpinning/5µs-8            32.2µs ± 0%    32.2µs ± 0%     -0.05%  (p=0.026 n=9+10)
    WakeupParallelSpinning/50µs-8            216µs ± 0%     216µs ± 0%     -0.12%  (p=0.004 n=10+10)
    WakeupParallelSpinning/1µs-8            20.6µs ± 0%    20.5µs ± 0%     -0.22%  (p=0.014 n=10+10)
    WakeupParallelSpinning/10µs-8           54.5µs ± 0%    54.2µs ± 1%     -0.57%  (p=0.000 n=10+10)
    CreateGoroutines-8                       213ns ± 1%     211ns ± 1%     -0.86%  (p=0.002 n=10+10)
    CreateGoroutinesCapture                 1.03µs ± 0%    1.02µs ± 0%     -0.91%  (p=0.000 n=10+10)
    CreateGoroutinesCapture-8               1.32µs ± 1%    1.31µs ± 1%     -1.06%  (p=0.001 n=10+9)
    CreateGoroutines                         188ns ± 0%     186ns ± 0%     -1.06%  (p=0.000 n=9+10)
    CreateGoroutinesParallel                 188ns ± 0%     186ns ± 0%     -1.27%  (p=0.000 n=8+10)
    WakeupParallelSyscall/0s                 210µs ± 3%     207µs ± 3%     -1.60%  (p=0.043 n=10+10)
    StackGrowthDeep                          121µs ± 1%     119µs ± 1%     -1.70%  (p=0.000 n=9+10)
    Matmult-8                               1.82ns ± 3%    1.78ns ± 3%     -2.16%  (p=0.020 n=10+10)
    WakeupParallelSyscall/20µs               281µs ± 3%     269µs ± 4%     -4.44%  (p=0.000 n=10+10)
    WakeupParallelSyscall/10µs               239µs ± 3%     228µs ± 9%     -4.70%  (p=0.001 n=10+10)
    GoroutineProfile/sparse-nil/idle-8       485µs ± 2%      12µs ± 4%    -97.56%  (p=0.000 n=10+10)
    GoroutineProfile/small-nil/idle-8        484µs ± 2%      12µs ± 1%    -97.60%  (p=0.000 n=10+7)
    GoroutineProfile/small-nil/loaded-8      487µs ± 2%      11µs ± 3%    -97.68%  (p=0.000 n=10+10)
    GoroutineProfile/sparse-nil/loaded-8     507µs ± 4%      11µs ± 6%    -97.78%  (p=0.000 n=10+10)
    GoroutineProfile/large-nil/idle-8        709µs ± 2%      11µs ± 4%    -98.38%  (p=0.000 n=10+10)
    GoroutineProfile/large-nil/loaded-8      717µs ± 2%      11µs ± 3%    -98.43%  (p=0.000 n=10+10)
    GoroutineProfile/sparse-nil/idle         465µs ± 3%       1µs ± 1%    -99.84%  (p=0.000 n=10+10)
    GoroutineProfile/small-nil/idle          493µs ± 3%       1µs ± 0%    -99.85%  (p=0.000 n=10+9)
    GoroutineProfile/large-nil/idle          716µs ± 1%       1µs ± 2%    -99.89%  (p=0.000 n=7+10)

    name                                  old alloc/op   new alloc/op   delta
    CreateGoroutinesCapture                   144B ± 0%      144B ± 0%       ~     (all equal)
    CreateGoroutinesCapture-8                 144B ± 0%      144B ± 0%       ~     (all equal)

    name                                  old allocs/op  new allocs/op  delta
    CreateGoroutinesCapture                   5.00 ± 0%      5.00 ± 0%       ~     (all equal)
    CreateGoroutinesCapture-8                 5.00 ± 0%      5.00 ± 0%       ~     (all equal)

    name                                  old p50-ns     new p50-ns     delta
    GoroutineProfile/small/loaded-8          1.01M ± 3%     3.87M ±45%   +282.15%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/loaded-8         1.02M ± 3%     2.43M ±41%   +138.42%  (p=0.000 n=10+10)
    GoroutineProfile/large/loaded-8          7.43M ±16%    17.28M ± 2%   +132.43%  (p=0.000 n=10+10)
    GoroutineProfile/small/idle               956k ± 0%     1559k ±16%    +63.03%  (p=0.000 n=10+10)
    GoroutineProfile/small/idle-8            1.01M ± 3%     1.45M ± 7%    +44.31%  (p=0.000 n=10+9)
    GoroutineProfile/sparse/idle              977k ± 1%     1399k ± 2%    +43.20%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/idle-8           1.00M ± 3%     1.41M ± 3%    +40.47%  (p=0.000 n=10+10)
    GoroutineProfile/large/idle-8            6.97M ± 1%     8.41M ±25%    +20.54%  (p=0.003 n=8+10)
    GoroutineProfile/large/idle              6.71M ± 1%     7.46M ± 4%    +11.15%  (p=0.000 n=10+10)
    GoroutineProfile/sparse-nil/idle-8        483k ± 3%       13k ± 3%    -97.41%  (p=0.000 n=10+9)
    GoroutineProfile/small-nil/idle-8         483k ± 2%       12k ± 1%    -97.43%  (p=0.000 n=10+8)
    GoroutineProfile/small-nil/loaded-8       484k ± 3%       10k ± 2%    -97.93%  (p=0.000 n=10+8)
    GoroutineProfile/sparse-nil/loaded-8      492k ± 2%       10k ± 4%    -97.97%  (p=0.000 n=10+8)
    GoroutineProfile/large-nil/idle-8         708k ± 2%       12k ±15%    -98.36%  (p=0.000 n=10+10)
    GoroutineProfile/large-nil/loaded-8       714k ± 2%       10k ± 2%    -98.60%  (p=0.000 n=10+8)
    GoroutineProfile/sparse-nil/idle          459k ± 1%        1k ± 1%    -99.85%  (p=0.000 n=10+10)
    GoroutineProfile/small-nil/idle           477k ± 1%        1k ± 0%    -99.85%  (p=0.000 n=10+9)
    GoroutineProfile/large-nil/idle           712k ± 1%        1k ± 1%    -99.90%  (p=0.000 n=7+10)

    name                                  old p90-ns     new p90-ns     delta
    GoroutineProfile/small/loaded-8          1.13M ±10%     7.49M ±35%   +562.07%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/loaded-8         1.10M ±12%     4.58M ±31%   +318.02%  (p=0.000 n=10+9)
    GoroutineProfile/large/loaded-8          8.78M ±24%    27.83M ± 2%   +217.00%  (p=0.000 n=10+10)
    GoroutineProfile/small/idle               967k ± 0%     2909k ±50%   +200.91%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/idle-8           1.02M ± 3%     1.96M ±76%    +92.99%  (p=0.000 n=10+10)
    GoroutineProfile/small/idle-8            1.07M ±17%     1.55M ±12%    +45.23%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/idle              992k ± 1%     1417k ± 3%    +42.79%  (p=0.000 n=9+10)
    GoroutineProfile/large/idle              6.73M ± 0%     7.99M ± 8%    +18.80%  (p=0.000 n=8+10)
    GoroutineProfile/large/idle-8            8.20M ±25%     9.18M ±25%       ~     (p=0.315 n=10+10)
    GoroutineProfile/sparse-nil/idle-8        495k ± 3%       13k ± 1%    -97.36%  (p=0.000 n=10+9)
    GoroutineProfile/small-nil/idle-8         494k ± 2%       13k ± 3%    -97.36%  (p=0.000 n=10+10)
    GoroutineProfile/small-nil/loaded-8       496k ± 2%       13k ± 1%    -97.41%  (p=0.000 n=10+10)
    GoroutineProfile/sparse-nil/loaded-8      544k ±11%       13k ± 1%    -97.62%  (p=0.000 n=10+9)
    GoroutineProfile/large-nil/idle-8         724k ± 1%       13k ± 3%    -98.20%  (p=0.000 n=10+10)
    GoroutineProfile/large-nil/loaded-8       729k ± 3%       13k ± 2%    -98.23%  (p=0.000 n=10+10)
    GoroutineProfile/sparse-nil/idle          476k ± 4%        1k ± 1%    -99.85%  (p=0.000 n=9+10)
    GoroutineProfile/small-nil/idle           537k ±10%        1k ± 0%    -99.87%  (p=0.000 n=10+9)
    GoroutineProfile/large-nil/idle           729k ± 0%        1k ± 1%    -99.90%  (p=0.000 n=7+10)

    name                                  old p99-ns     new p99-ns     delta
    GoroutineProfile/sparse/loaded-8         1.27M ±33%    20.49M ±17%  +1514.61%  (p=0.000 n=10+10)
    GoroutineProfile/small/loaded-8          1.37M ±29%    20.48M ±23%  +1399.35%  (p=0.000 n=10+10)
    GoroutineProfile/large/loaded-8          9.76M ±23%    39.98M ±22%   +309.52%  (p=0.000 n=10+8)
    GoroutineProfile/small/idle               976k ± 1%     3367k ±55%   +244.94%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/idle-8           1.03M ± 3%     2.50M ±65%   +142.30%  (p=0.000 n=10+10)
    GoroutineProfile/small/idle-8            1.17M ±34%     1.70M ±14%    +45.15%  (p=0.000 n=10+10)
    GoroutineProfile/sparse/idle             1.02M ± 3%     1.45M ± 4%    +42.64%  (p=0.000 n=9+10)
    GoroutineProfile/large/idle              6.92M ± 2%     9.00M ± 7%    +29.98%  (p=0.000 n=8+9)
    GoroutineProfile/large/idle-8            8.74M ±23%     9.90M ±24%       ~     (p=0.190 n=10+10)
    GoroutineProfile/sparse-nil/idle-8        508k ± 4%       16k ± 2%    -96.90%  (p=0.000 n=10+9)
    GoroutineProfile/small-nil/idle-8         508k ± 4%       16k ± 3%    -96.91%  (p=0.000 n=10+9)
    GoroutineProfile/small-nil/loaded-8       542k ± 5%       15k ±15%    -97.15%  (p=0.000 n=10+10)
    GoroutineProfile/sparse-nil/loaded-8      649k ±16%       15k ±18%    -97.67%  (p=0.000 n=10+10)
    GoroutineProfile/large-nil/idle-8         738k ± 2%       16k ± 2%    -97.86%  (p=0.000 n=10+10)
    GoroutineProfile/large-nil/loaded-8       765k ± 4%       15k ±17%    -98.03%  (p=0.000 n=10+10)
    GoroutineProfile/sparse-nil/idle          539k ±26%        1k ±17%    -99.84%  (p=0.000 n=10+10)
    GoroutineProfile/small-nil/idle           659k ±25%        1k ± 0%    -99.84%  (p=0.000 n=10+8)
    GoroutineProfile/large-nil/idle           760k ± 2%        1k ±22%    -99.88%  (p=0.000 n=9+10)

Fixes #33250
For #50794

Change-Id: I862a2bc4e991cec485f21a6fce4fca84f2c6435b
Reviewed-on: https://go-review.googlesource.com/c/go/+/387415
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Rhys Hiltner <rhys@justin.tv>
TryBot-Result: Gopher Robot <gobot@golang.org>