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runtime: fix check for pending GC work

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When findRunnable considers running a fractional mark worker, it first
checks if there's any work to be done; if there isn't there's no point
in running the worker because it will just reschedule immediately.
However, currently findRunnable just checks work.full and
work.partial, whereas getfull can *also* draw work from m.currentwbuf.
As a result, findRunnable may not start a worker even though there
actually is work.

This problem manifests itself in occasional failures of the
test/init1.go test. This test is unusual because it performs a large
amount of allocation without executing any write barriers, which means
there's nothing to force the pointers in currentwbuf out to the
work.partial/full lists where findRunnable can see them.

This change fixes this problem by making findRunnable also check for a
currentwbuf. This aligns findRunnable with trygetfull's notion of
whether or not there's work.

Change-Id: Ic76d22b7b5d040bc4f58a6b5975e9217650e66c4
Reviewed-on: https://go-review.googlesource.com/9299
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Austin Clements 2015-04-23 20:00:10 -04:00
parent 26eac917dc
commit d1cae6358c
1 changed files with 1 additions and 1 deletions
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2
src/runtime/mgc.go
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@ -501,7 +501,7 @@ func (c *gcControllerState) findRunnable(_p_ *p) *g {
// else for a while, so kick everything out of its run
// queue.
} else {
if work.full == 0 && work.partial == 0 {
if _p_.m.ptr().currentwbuf == 0 && work.full == 0 && work.partial == 0 {
// No work to be done right now. This can
// happen at the end of the mark phase when
// there are still assists tapering off. Don't