Messages in this thread | | | Date | Tue, 19 Nov 2013 15:05:42 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v5 2/4] MCS Lock: optimizations and extra comments |
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On Tue, Nov 19, 2013 at 02:57:41PM -0800, Tim Chen wrote: > On Tue, 2013-11-19 at 11:13 -0800, Paul E. McKenney wrote: > > On Fri, Nov 08, 2013 at 11:52:05AM -0800, Tim Chen wrote: > > > > > > +/* > > > + * Releases the lock. The caller should pass in the corresponding node that > > > + * was used to acquire the lock. > > > + */ > > > static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node) > > > { > > > struct mcs_spinlock *next = ACCESS_ONCE(node->next); > > > @@ -51,7 +60,7 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod > > > /* > > > * Release the lock by setting it to NULL > > > */ > > > - if (cmpxchg(lock, node, NULL) == node) > > > + if (likely(cmpxchg(lock, node, NULL) == node)) > > > > Agreed here as well. Takes a narrow race to hit this. > > > > So, did your testing exercise this path? If the answer is "yes", > > > Paul, > > I did some instrumentation and confirmed that the path in question has > been exercised. So this patch should be okay.
Very good!
Thanx, Paul
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