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runtime: decentralize mark done and mark termination

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This moves all of the mark 1 to mark 2 transition and mark termination
to the mark done transition function. This means these transitions are
now handled on the goroutine that detected mark completion. This also
means that the GC coordinator and the background completion barriers
are no longer used and various workarounds to yield to the coordinator
are no longer necessary. These will be removed in follow-up commits.

One consequence of this is that mark workers now need to be
preemptible when performing the mark done transition. This allows them
to stop the world and to perform the final clean-up steps of GC after
restarting the world. They are only made preemptible while performing
this transition, so if the worker findRunnableGCWorker would schedule
isn't available, we didn't want to schedule it anyway.

Fixes #11970.

Change-Id: I9203a2d6287eeff62d589ec02ad9cb1e29ddb837
Reviewed-on: https://go-review.googlesource.com/16391
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Austin Clements 2015-10-26 11:27:37 -04:00
parent d986bf2741
commit c99d7f7f85
4 changed files with 121 additions and 77 deletions
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11
src/runtime/proc.go
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@ -1057,6 +1057,8 @@ func mstart1() {
// memory barrier. GC uses this as a "ragged barrier."
//
// The caller must hold worldsema.
//
//go:systemstack
func forEachP(fn func(*p)) {
mp := acquirem()
_p_ := getg().m.p.ptr()
@ -1115,6 +1117,8 @@ func forEachP(fn func(*p)) {
for {
// Wait for 100us, then try to re-preempt in
// case of any races.
//
// Requires system stack.
if notetsleep(&sched.safePointNote, 100*1000) {
noteclear(&sched.safePointNote)
break
@ -1773,10 +1777,9 @@ top:
stop:
// We have nothing to do. If we're in the GC mark phase, can
// safely scan and blacken objects, can start a worker, and
// have work to do, run idle-time marking rather than give up
// the P.
if _p_ := _g_.m.p.ptr(); gcBlackenEnabled != 0 && _p_.gcBgMarkWorker != nil && (work.bgMark1.done == 0 || work.bgMark2.done == 0) && gcMarkWorkAvailable(_p_) {
// safely scan and blacken objects, and have work to do, run
// idle-time marking rather than give up the P.
if _p_ := _g_.m.p.ptr(); gcBlackenEnabled != 0 && _p_.gcBgMarkWorker != nil && gcMarkWorkAvailable(_p_) {
_p_.gcMarkWorkerMode = gcMarkWorkerIdleMode
gp := _p_.gcBgMarkWorker
casgstatus(gp, _Gwaiting, _Grunnable)