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Austin Clements 2a889b9d93 runtime: make stack re-scan O(# dirty stacks) 
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/20700
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
 		2016-04-26 23:40:13 +00:00
.github doc: update issue template 2016-03-09 00:52:16 +00:00
api api: update next.txt 2016-04-22 23:09:00 +00:00
doc spec: be more explicit about equivalence of empty string and absent field tags 2016-04-25 19:21:40 +00:00
lib/time misc: update timezone database to IANA 2016a 2016-02-03 03:14:59 +00:00
misc cmd/link: use gold when dynamic linking on arm64 2016-04-18 16:14:44 +00:00
src runtime: make stack re-scan O(# dirty stacks) 2016-04-26 23:40:13 +00:00
test cmd/compile: treat empty and absent struct field tags as identical 2016-04-25 21:28:45 +00:00
.gitattributes .gitattributes: prevent all magic line ending changes 2014-12-12 23:14:54 +00:00
.gitignore .gitignore: don't ignore y.output 2016-04-17 22:41:13 +00:00
AUTHORS A+C: manual updates 2016-01-08 06:02:39 +00:00
CONTRIBUTING.md doc: use new Gerrit URL and mention our instance in CONTRIBUTING.md 2016-03-09 00:52:42 +00:00
CONTRIBUTORS C: fix jbd's identity 2016-04-07 18:25:13 +00:00
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README.md

The Go Programming Language

Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.

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For documentation about how to install and use Go, visit https://golang.org/ or load doc/install-source.html in your web browser.

Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.

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To contribute, please read the contribution guidelines: https://golang.org/doc/contribute.html

Note that we do not accept pull requests and that we use the issue tracker for bug reports and proposals only. Please ask questions on https://forum.golangbridge.org or https://groups.google.com/forum/#!forum/golang-nuts.

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

--

Binary Distribution Notes

If you have just untarred a binary Go distribution, you need to set the environment variable $GOROOT to the full path of the go directory (the one containing this file). You can omit the variable if you unpack it into /usr/local/go, or if you rebuild from sources by running all.bash (see doc/install-source.html). You should also add the Go binary directory $GOROOT/bin to your shell's path.

For example, if you extracted the tar file into $HOME/go, you might put the following in your .profile:

export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin

See https://golang.org/doc/install or doc/install.html for more details.