linux-kernel - Re: [PATCH v2 2/5] mutex: Modify the way optimistic spinners are queued

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Date:	Sun, 2 Feb 2014 13:58:17 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Jason Low <jason.low2@...com>
Cc:	mingo@...hat.com, peterz@...radead.org, Waiman.Long@...com,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, riel@...hat.com,
	akpm@...ux-foundation.org, davidlohr@...com, hpa@...or.com,
	andi@...stfloor.org, aswin@...com, scott.norton@...com,
	chegu_vinod@...com
Subject: Re: [PATCH v2 2/5] mutex: Modify the way optimistic spinners are
 queued

On Tue, Jan 28, 2014 at 02:10:41PM -0800, Jason Low wrote:
> On Tue, 2014-01-28 at 12:23 -0800, Paul E. McKenney wrote:
> > On Tue, Jan 28, 2014 at 11:13:13AM -0800, Jason Low wrote:
> > >  		/*
> > >  		 * The cpu_relax() call is a compiler barrier which forces
> > > @@ -514,6 +511,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
> > >  		 */
> > >  		arch_mutex_cpu_relax();
> > >  	}
> > > +	mspin_unlock(MLOCK(lock), &node);
> > >  slowpath:
> > 
> > Are there any remaining goto statements to slowpath?  If so, they need
> > to release the lock.  If not, this label should be removed.
> 
> Yes, if the mutex_can_spin_on_owner() returns false, then the thread
> goes to directly slowpath, bypassing the optimistic spinning loop. In
> that case, the thread avoids acquiring the MCS lock, and doesn't unlock
> the MCS lock.

Got it, apologies for my confusion!

							Thanx, Paul

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