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Austin Clements b6c0934a9b runtime: cache two workbufs to reduce contention 
Currently the gcWork abstraction caches a single work buffer. As a
result, if a worker is putting and getting pointers right at the
boundary of a work buffer, it can flap between work buffers and
(potentially significantly) increase contention on the global work
buffer lists.

This change modifies gcWork to instead cache two work buffers and
switch off between them. This introduces one buffers' worth of
hysteresis and eliminates the above performance worst case by
amortizing the cost of getting or putting a work buffer over at least
one buffers' worth of work.

In practice, it's difficult to trigger this worst case with reasonably
large work buffers. On the garbage benchmark, this reduces the max
writes/sec to the global work list from 32K to 25K and the median from
6K to 5K. However, if a workload were to trigger this worst case
behavior, it could significantly drive up this contention.

This has negligible effects on the go1 benchmarks and slightly speeds
up the garbage benchmark.

name              old time/op  new time/op  delta
XBenchGarbage-12  5.90ms ± 3%  5.83ms ± 4%  -1.18%  (p=0.011 n=18+18)

name                      old time/op    new time/op    delta
BinaryTree17-12              3.22s ± 4%     3.17s ± 3%  -1.57%  (p=0.009 n=19+20)
Fannkuch11-12                2.44s ± 1%     2.53s ± 4%  +3.78%  (p=0.000 n=18+19)
FmtFprintfEmpty-12          50.2ns ± 2%    50.5ns ± 5%    ~     (p=0.631 n=19+20)
FmtFprintfString-12          167ns ± 1%     166ns ± 1%    ~     (p=0.141 n=20+20)
FmtFprintfInt-12             162ns ± 1%     159ns ± 1%  -1.80%  (p=0.000 n=20+20)
FmtFprintfIntInt-12          277ns ± 2%     263ns ± 1%  -4.78%  (p=0.000 n=20+18)
FmtFprintfPrefixedInt-12     240ns ± 1%     232ns ± 2%  -3.25%  (p=0.000 n=20+20)
FmtFprintfFloat-12           311ns ± 1%     315ns ± 2%  +1.17%  (p=0.000 n=20+20)
FmtManyArgs-12              1.05µs ± 2%    1.03µs ± 2%  -1.72%  (p=0.000 n=20+20)
GobDecode-12                8.65ms ± 1%    8.71ms ± 2%  +0.68%  (p=0.001 n=19+20)
GobEncode-12                6.51ms ± 1%    6.54ms ± 1%  +0.42%  (p=0.047 n=20+19)
Gzip-12                      318ms ± 2%     315ms ± 2%  -1.20%  (p=0.000 n=19+19)
Gunzip-12                   42.2ms ± 2%    42.1ms ± 1%    ~     (p=0.667 n=20+19)
HTTPClientServer-12         62.5µs ± 1%    62.4µs ± 1%    ~     (p=0.110 n=20+18)
JSONEncode-12               16.8ms ± 1%    16.8ms ± 2%    ~     (p=0.569 n=19+20)
JSONDecode-12               60.8ms ± 2%    59.8ms ± 1%  -1.69%  (p=0.000 n=19+19)
Mandelbrot200-12            3.87ms ± 1%    3.85ms ± 0%  -0.61%  (p=0.001 n=20+17)
GoParse-12                  3.76ms ± 2%    3.76ms ± 1%    ~     (p=0.698 n=20+20)
RegexpMatchEasy0_32-12       100ns ± 2%     101ns ± 2%    ~     (p=0.065 n=19+20)
RegexpMatchEasy0_1K-12       342ns ± 2%     333ns ± 1%  -2.82%  (p=0.000 n=20+19)
RegexpMatchEasy1_32-12      83.3ns ± 2%    83.2ns ± 2%    ~     (p=0.692 n=20+19)
RegexpMatchEasy1_1K-12       498ns ± 2%     490ns ± 1%  -1.52%  (p=0.000 n=18+20)
RegexpMatchMedium_32-12      131ns ± 2%     131ns ± 2%    ~     (p=0.464 n=20+18)
RegexpMatchMedium_1K-12     39.3µs ± 2%    39.6µs ± 1%  +0.77%  (p=0.000 n=18+19)
RegexpMatchHard_32-12       2.04µs ± 2%    2.06µs ± 1%  +0.69%  (p=0.009 n=19+20)
RegexpMatchHard_1K-12       61.4µs ± 2%    62.1µs ± 1%  +1.21%  (p=0.000 n=19+20)
Revcomp-12                   534ms ± 1%     529ms ± 1%  -0.97%  (p=0.000 n=19+16)
Template-12                 70.4ms ± 2%    70.0ms ± 1%    ~     (p=0.070 n=19+19)
TimeParse-12                 359ns ± 3%     344ns ± 1%  -4.15%  (p=0.000 n=19+19)
TimeFormat-12                357ns ± 1%     361ns ± 2%  +1.05%  (p=0.002 n=20+20)
[Geo mean]                  62.4µs         62.0µs       -0.56%

name                      old speed      new speed      delta
GobDecode-12              88.7MB/s ± 1%  88.1MB/s ± 2%  -0.68%  (p=0.001 n=19+20)
GobEncode-12               118MB/s ± 1%   117MB/s ± 1%  -0.42%  (p=0.046 n=20+19)
Gzip-12                   60.9MB/s ± 2%  61.7MB/s ± 2%  +1.21%  (p=0.000 n=19+19)
Gunzip-12                  460MB/s ± 2%   461MB/s ± 1%    ~     (p=0.661 n=20+19)
JSONEncode-12              116MB/s ± 1%   115MB/s ± 2%    ~     (p=0.555 n=19+20)
JSONDecode-12             31.9MB/s ± 2%  32.5MB/s ± 1%  +1.72%  (p=0.000 n=19+19)
GoParse-12                15.4MB/s ± 2%  15.4MB/s ± 1%    ~     (p=0.653 n=20+20)
RegexpMatchEasy0_32-12     317MB/s ± 2%   315MB/s ± 2%    ~     (p=0.141 n=19+20)
RegexpMatchEasy0_1K-12    2.99GB/s ± 2%  3.07GB/s ± 1%  +2.86%  (p=0.000 n=20+19)
RegexpMatchEasy1_32-12     384MB/s ± 2%   385MB/s ± 2%    ~     (p=0.672 n=20+19)
RegexpMatchEasy1_1K-12    2.06GB/s ± 2%  2.09GB/s ± 1%  +1.54%  (p=0.000 n=18+20)
RegexpMatchMedium_32-12   7.62MB/s ± 2%  7.63MB/s ± 2%    ~     (p=0.800 n=20+18)
RegexpMatchMedium_1K-12   26.0MB/s ± 1%  25.8MB/s ± 1%  -0.77%  (p=0.000 n=18+19)
RegexpMatchHard_32-12     15.7MB/s ± 2%  15.6MB/s ± 1%  -0.69%  (p=0.010 n=19+20)
RegexpMatchHard_1K-12     16.7MB/s ± 2%  16.5MB/s ± 1%  -1.19%  (p=0.000 n=19+20)
Revcomp-12                 476MB/s ± 1%   481MB/s ± 1%  +0.97%  (p=0.000 n=19+16)
Template-12               27.6MB/s ± 2%  27.7MB/s ± 1%    ~     (p=0.071 n=19+19)
[Geo mean]                99.1MB/s       99.3MB/s       +0.27%

Change-Id: I68bcbf74ccb716cd5e844a554f67b679135105e6
Reviewed-on: https://go-review.googlesource.com/16042
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
 		2015-11-03 19:12:10 +00:00
api api: update next.txt 2015-10-12 23:00:00 +00:00
doc doc/go1.6.txt: mention possible GOTRACEBACK change 2015-10-30 18:43:53 +00:00
lib/time lib/time: update to IANA release 2015e. 2015-07-22 02:56:31 +00:00
misc misc/ios: fix an error when getenv encounters unset variable 2015-11-03 15:17:35 +00:00
src runtime: cache two workbufs to reduce contention 2015-11-03 19:12:10 +00:00
test runtime: fix finalization and profiling of tiny allocations 2015-11-03 18:57:18 +00:00
.gitattributes .gitattributes: prevent all magic line ending changes 2014-12-12 23:14:54 +00:00
.gitignore .gitignore: ignore y.output 2015-06-10 00:28:52 +00:00
AUTHORS A+C: automated updates 2015-09-10 00:59:04 +00:00
CONTRIBUTING.md doc: suggest security@golang.org for reporting security issues 2015-06-26 09:53:36 +00:00
CONTRIBUTORS C: Add Brian Gitonga Marete's Google email address (Google CLA). 2015-10-09 15:21:30 +00:00
LICENSE doc: update licensing text one more time 2012-03-27 15:09:13 +11:00
PATENTS LICENSE: separate, change PATENTS text 2010-12-06 16:31:59 -05:00
README.md readme: emphasize issue tracker is for bugs/proposals 2015-10-02 18:44:14 +00:00
favicon.ico godoc: update favicon 2012-10-11 17:02:36 +11:00
robots.txt godoc: serve robots.txt raw 2011-02-19 05:46:20 +11:00

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.

Go is the work of hundreds of contributors. We appreciate your help!

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.