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runtime: make garbage collector faster by deleting code again

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Remove GC bitmap backward scanning.
This was already done once in https://golang.org/cl/5530074/
Still makes GC a bit faster.
On the garbage benchmark, before:
        gc-pause-one=237345195
        gc-pause-total=4746903
        cputime=32427775
        time=32458208
after:
        gc-pause-one=235484019
        gc-pause-total=4709680
        cputime=31861965
        time=31877772
Also prepares mgc0.c for future changes.

R=golang-codereviews, khr, khr
CC=golang-codereviews, rsc
https://golang.org/cl/105380043
This commit is contained in:
Dmitriy Vyukov 2014-06-27 18:19:02 -07:00
parent 84a36434d9
commit 03f2189a1b
1 changed files with 2 additions and 27 deletions
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29
src/pkg/runtime/mgc0.c
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@ -270,7 +270,7 @@ static bool
markonly(void *obj)
{
byte *p;
uintptr *bitp, bits, shift, x, xbits, off, j;
uintptr *bitp, bits, shift, x, xbits, off;
MSpan *s;
PageID k;
@ -298,18 +298,6 @@ markonly(void *obj)
goto found;
}
// Pointing just past the beginning?
// Scan backward a little to find a block boundary.
for(j=shift; j-->0; ) {
if(((xbits>>j) & (bitAllocated|bitBlockBoundary)) != 0) {
shift = j;
bits = xbits>>shift;
if(CollectStats)
runtime·xadd64(&gcstats.markonly.foundword, 1);
goto found;
}
}
// Otherwise consult span table to find beginning.
// (Manually inlined copy of MHeap_LookupMaybe.)
k = (uintptr)obj>>PageShift;
@ -424,7 +412,7 @@ static void
flushptrbuf(Scanbuf *sbuf)
{
byte *p, *arena_start, *obj;
uintptr size, *bitp, bits, shift, j, x, xbits, off, nobj, ti, n;
uintptr size, *bitp, bits, shift, x, xbits, off, nobj, ti, n;
MSpan *s;
PageID k;
Obj *wp;
@ -496,19 +484,6 @@ flushptrbuf(Scanbuf *sbuf)
ti = 0;
// Pointing just past the beginning?
// Scan backward a little to find a block boundary.
for(j=shift; j-->0; ) {
if(((xbits>>j) & (bitAllocated|bitBlockBoundary)) != 0) {
obj = (byte*)obj - (shift-j)*PtrSize;
shift = j;
bits = xbits>>shift;
if(CollectStats)
runtime·xadd64(&gcstats.flushptrbuf.foundword, 1);
goto found;
}
}
// Otherwise consult span table to find beginning.
// (Manually inlined copy of MHeap_LookupMaybe.)
k = (uintptr)obj>>PageShift;