Messages in this thread | | | Date | Wed, 15 Jun 2016 15:08:48 -0400 | From | Waiman Long <> | Subject | Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier |
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On 06/15/2016 01:12 PM, Peter Zijlstra wrote: > On Wed, Jun 15, 2016 at 09:56:59AM -0700, Davidlohr Bueso wrote: >> On Tue, 14 Jun 2016, Waiman Long wrote: >>> +++ b/kernel/locking/osq_lock.c >>> @@ -115,7 +115,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) >>> * cmpxchg in an attempt to undo our queueing. >>> */ >>> >>> - while (!READ_ONCE(node->locked)) { >>> + while (!smp_load_acquire(&node->locked)) { >> Hmm this being a polling path, that barrier can get pretty expensive and >> last I checked it was unnecessary: > I think he'll go rely on it later on. > > In any case, its fairly simple to cure, just add > smp_acquire__after_ctrl_dep() at the end. If we bail because > need_resched() we don't need the acquire I think.
Yes, I only need the acquire barrier when the locking is successful. Thanks for the suggestion. I will make the change accordingly.
Cheers, Longman
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