diff options
| author | Nicholas Mc Guire <der.herr@hofr.at> | 2015-01-23 12:41:47 +0100 |
|---|---|---|
| committer | Moyster <oysterized@gmail.com> | 2016-08-26 20:20:23 +0200 |
| commit | c941b10f69f31a4fbbbaf99d8161062b65a911a0 (patch) | |
| tree | 2d2950f5fc65d8438c55216dc43f261b4c293964 /kernel/sched | |
| parent | 478c700c01cb041a95a4540915717c3012d1e5b2 (diff) | |
sched/completion: Add lock-free checking of the blocking case
The "thread would block" case can be checked without grabbing ->wait.lock.
[ If the check does not return early then grab the lock and recheck.
A memory barrier is not needed as complete() and complete_all() imply
a barrier.
The ACCESS_ONCE() is needed for calls in a loop that, if inlined, could
optimize out the re-fetching of x->done. ]
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1422013307-13200-1-git-send-email-der.herr@hofr.at
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Stefan Guendhoer <stefan@guendhoer.com>
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/core.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 844dfcc9c..1ce7c15e8 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3823,6 +3823,15 @@ bool try_wait_for_completion(struct completion *x) unsigned long flags; int ret = 1; + /* + * Since x->done will need to be locked only + * in the non-blocking case, we check x->done + * first without taking the lock so we can + * return early in the blocking case. + */ + if (!ACCESS_ONCE(x->done)) + return 0; + spin_lock_irqsave(&x->wait.lock, flags); if (!x->done) ret = 0; |