Re: [PATCH v5 2/4] MCS Lock: optimizations and extra comments

[Paul E. McKenney]

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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