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Austin Clements 1870572180 runtime: enlarge GC work buffer size
Currently the GC work buffers are only 256 bytes and hence can record
only 24 64-bit pointer. They were reduced from 4K in commits db7fd1c
and a15818f as a way to minimize the amount of work the per-P workbuf
caches could "hide" from the mark phase and carry in to the mark
termination phase. However, this approach wasn't very robust and we
later added a "mark 2" phase to address this problem head-on.

Because of mark 2, there's now no benefit to having very small work
buffers. But there are plenty of downsides: small work buffers
increase contention on the work lists, increase the frequency and
hence net overhead of acquiring and releasing work buffers, and
somewhat increase memory overhead of the GC.

This commit expands work buffers back to 4K (504 64-bit pointers).
This reduces the rate of writes to work.full in the garbage benchmark
from a peak of ~780,000 writes/sec to a peak of ~32,000 writes/sec.

This has negligible effect on the go1 benchmarks. It slightly slows
down the garbage benchmark.

name              old time/op  new time/op  delta
XBenchGarbage-12  5.37ms ± 5%  5.60ms ± 2%  +4.37%  (p=0.000 n=20+20)

Change-Id: Ic9cc28e7a125d23d9faf4f5e690fb8aa9bcdfb28
Reviewed-on: https://go-review.googlesource.com/15893
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2015-11-03 15:53:38 +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: enlarge GC work buffer size 2015-11-03 15:53:38 +00:00
test test: use go:noinline consistently 2015-11-03 02:01:34 +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
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README.md readme: emphasize issue tracker is for bugs/proposals 2015-10-02 18:44:14 +00:00
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