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.atSigned-off-by:
Ingo Molnar <mingo@kernel.org>
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