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runtime: mark with non-atomic operations when GOMAXPROCS=1

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Perf builders show 3-5% GC pause increase with GOMAXPROCS=1 when marking with atomic ops:
http://goperfd.appspot.com/perfdetail?commit=a8a6e765d6a87f7ccb71fd85a60eb5a821151f85&commit0=3b864e02b987171e05e2e9d0840b85b5b6476386&kind=builder&builder=linux-amd64&benchmark=http

LGTM=rlh
R=golang-codereviews, rlh
CC=dave, golang-codereviews, khr, rsc
https://golang.org/cl/128340043
This commit is contained in:
Dmitriy Vyukov 2014-08-16 09:07:55 +04:00
parent 78cc89ce67
commit c6fe53a230
1 changed files with 2 additions and 1 deletions
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3
src/pkg/runtime/mgc0.c
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@ -451,7 +451,8 @@ scanblock(byte *b, uintptr n, byte *ptrmask)
// quadruple is already marked. Otherwise we resort to CAS
// loop for marking.
bits8 = xbits>>(shift&~7);
if((bits8&(bitMask|(bitMask<<gcBits))) != (bitBoundary|(bitBoundary<<gcBits)))
if((bits8&(bitMask|(bitMask<<gcBits))) != (bitBoundary|(bitBoundary<<gcBits)) ||
work.nproc == 1)
((uint8*)bitp)[shift/8] = bits8 | (bitMarked<<(shift&7));
else {
for(;;) {