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runtime: eliminate write barriers from dropg

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Currently this contains no write barriers because it's writing nil
pointers, but with the hybrid barrier, even these will produce write
barriers. However, since these are *gs and *ms, they don't need write
barriers, so we can simply eliminate them.

Updates #17503.

Change-Id: Ib188a60492c5cfb352814bf9b2bcb2941fb7d6c0
Reviewed-on: https://go-review.googlesource.com/31570
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2016-10-19 16:00:07 -04:00
parent 85c22bc3a5
commit 8044b77a57
2 changed files with 18 additions and 2 deletions
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4
src/runtime/proc.go
View File

@ -2175,8 +2175,8 @@ top:
func dropg() {
_g_ := getg()
_g_.m.curg.m = nil
_g_.m.curg = nil
setMNoWB(&_g_.m.curg.m, nil)
setGNoWB(&_g_.m.curg, nil)
}
func parkunlock_c(gp *g, lock unsafe.Pointer) bool {

16
src/runtime/runtime2.go
View File

@ -205,6 +205,14 @@ func (gp *guintptr) cas(old, new guintptr) bool {
return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
}
// setGNoWB performs *gp = new without a write barrier.
// For times when it's impractical to use a guintptr.
//go:nosplit
//go:nowritebarrier
func setGNoWB(gp **g, new *g) {
(*guintptr)(unsafe.Pointer(gp)).set(new)
}
type puintptr uintptr
//go:nosplit
@ -221,6 +229,14 @@ func (mp muintptr) ptr() *m { return (*m)(unsafe.Pointer(mp)) }
//go:nosplit
func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }
// setMNoWB performs *mp = new without a write barrier.
// For times when it's impractical to use an muintptr.
//go:nosplit
//go:nowritebarrier
func setMNoWB(mp **m, new *m) {
(*muintptr)(unsafe.Pointer(mp)).set(new)
}
type gobuf struct {
// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
sp uintptr