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runtime: Add prefetch to allocation code

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The routine mallocgc retrieves objects from freelists. Prefetch
the object that will be returned in the next call to mallocgc.
Experiments indicate that this produces a 1% improvement when using
prefetchnta and less when using prefetcht0, prefetcht1, or prefetcht2.

Benchmark numbers indicate a 1% improvement over no
prefetch, much less over prefetcht0, prefetcht1, and prefetcht2.
These numbers were for the garbage benchmark with MAXPROCS=4
no prefetch                          >> 5.96 / 5.77 / 5.89
prefetcht0(uintptr(v.ptr().next))    >> 5.88 / 6.17 / 5.84
prefetcht1(uintptr(v.ptr().next))    >> 5.88 / 5.89 / 5.91
prefetcht2(uintptr(v.ptr().next))    >> 5.87 / 6.47 / 5.92
prefetchnta(uintptr(v.ptr().next))   >> 5.72 / 5.84 / 5.85

Change-Id: I54e07172081cccb097d5b5ce8789d74daa055ed9
Reviewed-on: https://go-review.googlesource.com/5350
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Rick Hudson 2015-02-19 18:11:24 -05:00
parent 96333a7e48
commit 99482f2f9e
1 changed files with 4 additions and 2 deletions
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6
src/runtime/malloc.go
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@ -553,7 +553,8 @@ func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
} }
s.freelist = v.ptr().next s.freelist = v.ptr().next
s.ref++ s.ref++
//TODO: prefetch v.next // prefetchnta offers best performance, see change list message.
prefetchnta(uintptr(v.ptr().next))
x = unsafe.Pointer(v) x = unsafe.Pointer(v)
(*[2]uint64)(x)[0] = 0 (*[2]uint64)(x)[0] = 0
(*[2]uint64)(x)[1] = 0 (*[2]uint64)(x)[1] = 0
@ -584,7 +585,8 @@ func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
} }
s.freelist = v.ptr().next s.freelist = v.ptr().next
s.ref++ s.ref++
//TODO: prefetch // prefetchnta offers best performance, see change list message.
prefetchnta(uintptr(v.ptr().next))
x = unsafe.Pointer(v) x = unsafe.Pointer(v)
if flags&flagNoZero == 0 { if flags&flagNoZero == 0 {
v.ptr().next = 0 v.ptr().next = 0