code review 4693042: runtime: eliminate false sharing during stack growth

runtime: eliminate false sharing during stack growth
Remove static variable from runtime·oldstack().
Benchmark results on HP Z600 (2 x Xeon E5620, 8 HT cores, 2.40GHz)
are as follows (with CL 4657091 applied):
benchmark                                        old ns/op    new ns/op    delta
BenchmarkStackGrowth                               1183.00      1180.00   -0.25%
BenchmarkStackGrowth-2                             1249.00      1211.00   -3.04%
BenchmarkStackGrowth-4                              954.00       805.00  -15.62%
BenchmarkStackGrowth-8                              701.00       683.00   -2.57%
BenchmarkStackGrowth-16                             465.00       415.00  -10.75%

[dvyukov, 2011-07-11 14:14:45]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[rsc, 2011-07-12 05:27:39]

Please revert this change.
Then s/static // on the goid declaration
and insert USED(goid) on the line after the
assignment.

[dvyukov, 2011-07-12 10:47:33]

Hello rsc@golang.org (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2011-07-12 16:16:36]

http://codereview.appspot.com/4693042/diff/12001/src/pkg/runtime/proc.c
File src/pkg/runtime/proc.c (left):

http://codereview.appspot.com/4693042/diff/12001/src/pkg/runtime/proc.c#oldco...
src/pkg/runtime/proc.c:706: //printf("oldstack m->cret=%p\n", m->cret);
This printf isn't bothering anyone.  Please put it back.  
It matches the commented out one in newstack,
and when the stack code breaks they're very important.

[dvyukov, 2011-07-12 16:36:17]

Hello rsc@golang.org (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2011-07-12 16:38:39]

LGTM

[dvyukov, 2011-07-12 17:45:52]

Hello rsc@golang.org (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2011-07-12 17:56:26]

*** Submitted as c87c2f280a95 ***

runtime: eliminate false sharing during stack growth
Remove static variable from runtime·oldstack().
Benchmark results on HP Z600 (2 x Xeon E5620, 8 HT cores, 2.40GHz)
are as follows (with CL 4657091 applied):
benchmark                                        old ns/op    new ns/op    delta
BenchmarkStackGrowth                               1183.00      1180.00   -0.25%
BenchmarkStackGrowth-2                             1249.00      1211.00   -3.04%
BenchmarkStackGrowth-4                              954.00       805.00  -15.62%
BenchmarkStackGrowth-8                              701.00       683.00   -2.57%
BenchmarkStackGrowth-16                             465.00       415.00  -10.75%

R=rsc
CC=golang-dev
http://codereview.appspot.com/4693042

Committer: Russ Cox <rsc@golang.org>