From 44106a088077da9e32bf038beff4a42cd8b88a7a Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Fri, 8 Aug 2014 20:52:11 +0400
Subject: [PATCH] runtime: bump MaxGcprocs to 32 There was a number of
 improvements related to GC parallelization: 1. Parallel roots/stacks
 scanning. 2. Parallel stack shrinking. 3. Per-thread workbuf caches. 4.
 Workset reduction. Currently 32 threads work well. go.benchmarks:garbage
 benchmark on 2 x Intel Xeon E5-2690 (16 HT cores)

1 thread/1 processor:
time=16405255
cputime=16386223
gc-pause-one=546793975
gc-pause-total=3280763

2 threads/1 processor:
time=9043497
cputime=18075822
gc-pause-one=331116489
gc-pause-total=2152257

4 threads/1 processor:
time=4882030
cputime=19421337
gc-pause-one=174543105
gc-pause-total=1134530

8 threads/1 processor:
time=4134757
cputime=20097075
gc-pause-one=158680588
gc-pause-total=1015555

16 threads/1 processor + HT:
time=2006706
cputime=31960509
gc-pause-one=75425744
gc-pause-total=460097

16 threads/2 processors:
time=1513373
cputime=23805571
gc-pause-one=56630946
gc-pause-total=345448

32 threads/2 processors + HT:
time=1199312
cputime=37592764
gc-pause-one=48945064
gc-pause-total=278986

LGTM=rlh
R=golang-codereviews, tracey.brendan, rlh
CC=golang-codereviews, khr, rsc
https://golang.org/cl/123920043
---
 src/pkg/runtime/malloc.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/pkg/runtime/malloc.h b/src/pkg/runtime/malloc.h
index 593e9b885b9fd..556d6d4c03171 100644
--- a/src/pkg/runtime/malloc.h
+++ b/src/pkg/runtime/malloc.h
@@ -141,8 +141,8 @@ enum
 	// Max number of threads to run garbage collection.
 	// 2, 3, and 4 are all plausible maximums depending
 	// on the hardware details of the machine.  The garbage
-	// collector scales well to 8 cpus.
-	MaxGcproc = 8,
+	// collector scales well to 32 cpus.
+	MaxGcproc = 32,
 };
 
 // Maximum memory allocation size, a hint for callers.