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runtime: use multiply instead of divide in heapBitsForObject

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These benchmarks show the effect of the combination of this change
and Rick's pending CL 6665. Code with interior pointers is helped
much more than code without, but even code without doesn't suffer
too badly.

benchmark                          old ns/op      new ns/op      delta
BenchmarkBinaryTree17              6989407768     6851728175     -1.97%
BenchmarkFannkuch11                4416250775     4405762558     -0.24%
BenchmarkFmtFprintfEmpty           134            130            -2.99%
BenchmarkFmtFprintfString          491            402            -18.13%
BenchmarkFmtFprintfInt             430            420            -2.33%
BenchmarkFmtFprintfIntInt          748            663            -11.36%
BenchmarkFmtFprintfPrefixedInt     602            534            -11.30%
BenchmarkFmtFprintfFloat           728            699            -3.98%
BenchmarkFmtManyArgs               2528           2507           -0.83%
BenchmarkGobDecode                 17448191       17749756       +1.73%
BenchmarkGobEncode                 14579824       14370183       -1.44%
BenchmarkGzip                      656489990      652669348      -0.58%
BenchmarkGunzip                    141254147      141099278      -0.11%
BenchmarkHTTPClientServer          94111          93738          -0.40%
BenchmarkJSONEncode                36305013       36696440       +1.08%
BenchmarkJSONDecode                124652000      128176454      +2.83%
BenchmarkMandelbrot200             6009333        5997093        -0.20%
BenchmarkGoParse                   7651583        7623494        -0.37%
BenchmarkRegexpMatchEasy0_32       213            213            +0.00%
BenchmarkRegexpMatchEasy0_1K       511            494            -3.33%
BenchmarkRegexpMatchEasy1_32       186            187            +0.54%
BenchmarkRegexpMatchEasy1_1K       1834           1827           -0.38%
BenchmarkRegexpMatchMedium_32      427            412            -3.51%
BenchmarkRegexpMatchMedium_1K      154841         153086         -1.13%
BenchmarkRegexpMatchHard_32        7473           7478           +0.07%
BenchmarkRegexpMatchHard_1K        233587         232272         -0.56%
BenchmarkRevcomp                   918797689      944528032      +2.80%
BenchmarkTemplate                  167665081      167773121      +0.06%
BenchmarkTimeParse                 631            636            +0.79%
BenchmarkTimeFormat                672            666            -0.89%

Change-Id: Ia923de3cdb3993b640fe0a02cbe2c7babc16f32c
Reviewed-on: https://go-review.googlesource.com/6782
Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Russ Cox 2015-03-04 11:34:50 -05:00
parent 81d4072eb0
commit 9feb24f3ed
3 changed files with 82 additions and 1 deletions
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10
src/runtime/mheap.go
View file

@ -101,11 +101,14 @@ type mspan struct {
// if sweepgen == h->sweepgen, the span is swept and ready to use
// h->sweepgen is incremented by 2 after every GC
sweepgen uint32
divMul uint32 // for divide by elemsize - divMagic.mul
ref uint16 // capacity - number of objects in freelist
sizeclass uint8 // size class
incache bool // being used by an mcache
state uint8 // mspaninuse etc
needzero uint8 // needs to be zeroed before allocation
divShift uint8 // for divide by elemsize - divMagic.shift
divShift2 uint8 // for divide by elemsize - divMagic.shift2
elemsize uintptr // computed from sizeclass or from npages
unusedsince int64 // first time spotted by gc in mspanfree state
npreleased uintptr // number of pages released to the os
@ -385,8 +388,15 @@ func mHeap_Alloc_m(h *mheap, npage uintptr, sizeclass int32, large bool) *mspan
s.sizeclass = uint8(sizeclass)
if sizeclass == 0 {
s.elemsize = s.npages << _PageShift
s.divShift = 0
s.divMul = 0
s.divShift2 = 0
} else {
s.elemsize = uintptr(class_to_size[sizeclass])
m := &class_to_divmagic[sizeclass]
s.divShift = m.shift
s.divMul = m.mul
s.divShift2 = m.shift2
}
// update stats, sweep lists