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dvyukov opened this issue Sep 1, 2014 · 3 comments
Closed

runtime: GC performance regression #8625

dvyukov opened this issue Sep 1, 2014 · 3 comments
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FrozenDueToAge Performance
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Go1.4

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@dvyukov
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dvyukov commented Sep 1, 2014 

According to perf dashboard, change "112570044 cmd/gc, runtime: treat slices and
strings like pointers in garbage collection"
(https://golang.org/cl/112570044) has lead to 10-20% GC performance degradation:

http://build.golang.org/perfdetail?commit=caab29a25f686946a383ec31d2ea6408265aa466&;commit0=6d5c17d94e9ddcd8ca450ac62f84cf9ddb436b65&builder=windows-amd64-perf&benchmark=http

It looks like some unlucky code generation issue. Probably replacing the switch with
if-else will restore the performance.
@gopherbot
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Comment 1:

CL https://golang.org/cl/152170043 mentions this issue.

@gopherbot
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Comment 2:

CL https://golang.org/cl/153990043 mentions this issue.

@dvyukov
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dvyukov commented Oct 8, 2014

Comment 3:

This issue was closed by revision b8fdaaf.

Status changed to Fixed.

@rsc rsc added this to the Go1.4 milestone Apr 14, 2015
@rsc rsc removed the release-go1.4 label Apr 14, 2015
@golang golang locked and limited conversation to collaborators Jun 25, 2016
wheatman pushed a commit to wheatman/go-akaros that referenced this issue Jun 25, 2018
@dvyukov @wheatman
runtime: faster GC scan
1ecad8c 
The change contains 3 spot optimizations to scan loop:
1. Don't use byte vars, use uintptr's instead.
This seems to alleviate some codegen issue,
and alone accounts to a half of speedup.
2. Remove bitmap cache. Currently we cache only 1 byte,
so caching is not particularly effective anyway.
Removal of the cache simplifies code and positively affects regalloc.
3. Replace BitsMultiword switch with if and
do debug checks only in Debug mode.
I've benchmarked changes separately and ensured that
each of them provides speedup on top of the previous one.
This change as a whole fixes the unintentional regressions
of scan loop that were introduced during development cycle.
Fixes golang#8625.
Fixes golang#8565.

On go.benchmarks/garbage benchmark:
GOMAXPROCS=1
time:		-3.13%
cputime:	-3.22%
gc-pause-one:	-15.71%
gc-pause-total:	-15.71%

GOMAXPROCS=32
time:		-1.96%
cputime:	-4.43%
gc-pause-one:	-6.22%
gc-pause-total:	-6.22%

LGTM=khr, rsc
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/153990043
wheatman pushed a commit to wheatman/go-akaros that referenced this issue Jun 26, 2018
@dvyukov @wheatman
runtime: faster GC scan
4d848fd 
The change contains 3 spot optimizations to scan loop:
1. Don't use byte vars, use uintptr's instead.
This seems to alleviate some codegen issue,
and alone accounts to a half of speedup.
2. Remove bitmap cache. Currently we cache only 1 byte,
so caching is not particularly effective anyway.
Removal of the cache simplifies code and positively affects regalloc.
3. Replace BitsMultiword switch with if and
do debug checks only in Debug mode.
I've benchmarked changes separately and ensured that
each of them provides speedup on top of the previous one.
This change as a whole fixes the unintentional regressions
of scan loop that were introduced during development cycle.
Fixes golang#8625.
Fixes golang#8565.

On go.benchmarks/garbage benchmark:
GOMAXPROCS=1
time:		-3.13%
cputime:	-3.22%
gc-pause-one:	-15.71%
gc-pause-total:	-15.71%

GOMAXPROCS=32
time:		-1.96%
cputime:	-4.43%
gc-pause-one:	-6.22%
gc-pause-total:	-6.22%

LGTM=khr, rsc
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/153990043
wheatman pushed a commit to wheatman/go-akaros that referenced this issue Jul 9, 2018
@dvyukov @wheatman
runtime: faster GC scan
fcc1df7 
The change contains 3 spot optimizations to scan loop:
1. Don't use byte vars, use uintptr's instead.
This seems to alleviate some codegen issue,
and alone accounts to a half of speedup.
2. Remove bitmap cache. Currently we cache only 1 byte,
so caching is not particularly effective anyway.
Removal of the cache simplifies code and positively affects regalloc.
3. Replace BitsMultiword switch with if and
do debug checks only in Debug mode.
I've benchmarked changes separately and ensured that
each of them provides speedup on top of the previous one.
This change as a whole fixes the unintentional regressions
of scan loop that were introduced during development cycle.
Fixes golang#8625.
Fixes golang#8565.

On go.benchmarks/garbage benchmark:
GOMAXPROCS=1
time:		-3.13%
cputime:	-3.22%
gc-pause-one:	-15.71%
gc-pause-total:	-15.71%

GOMAXPROCS=32
time:		-1.96%
cputime:	-4.43%
gc-pause-one:	-6.22%
gc-pause-total:	-6.22%

LGTM=khr, rsc
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/153990043
wheatman pushed a commit to wheatman/go-akaros that referenced this issue Jul 30, 2018
@dvyukov @wheatman
runtime: faster GC scan
278db01 
The change contains 3 spot optimizations to scan loop:
1. Don't use byte vars, use uintptr's instead.
This seems to alleviate some codegen issue,
and alone accounts to a half of speedup.
2. Remove bitmap cache. Currently we cache only 1 byte,
so caching is not particularly effective anyway.
Removal of the cache simplifies code and positively affects regalloc.
3. Replace BitsMultiword switch with if and
do debug checks only in Debug mode.
I've benchmarked changes separately and ensured that
each of them provides speedup on top of the previous one.
This change as a whole fixes the unintentional regressions
of scan loop that were introduced during development cycle.
Fixes golang#8625.
Fixes golang#8565.

On go.benchmarks/garbage benchmark:
GOMAXPROCS=1
time:		-3.13%
cputime:	-3.22%
gc-pause-one:	-15.71%
gc-pause-total:	-15.71%

GOMAXPROCS=32
time:		-1.96%
cputime:	-4.43%
gc-pause-one:	-6.22%
gc-pause-total:	-6.22%

LGTM=khr, rsc
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/153990043
This issue was closed.
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