Date: Sun, 2 Feb 2014 13:58:17 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Jason Low <jason.low2@hp.com>
Cc: mingo@redhat.com, peterz@infradead.org, Waiman.Long@hp.com,
        torvalds@linux-foundation.org, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, riel@redhat.com,
        akpm@linux-foundation.org, davidlohr@hp.com, hpa@zytor.com,
        andi@firstfloor.org, aswin@hp.com, scott.norton@hp.com,
        chegu_vinod@hp.com
Subject: Re: [PATCH v2 2/5] mutex: Modify the way optimistic spinners are
 queued
Message-ID: <20140202215817.GE4333@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <1390936396-3962-1-git-send-email-jason.low2@hp.com>
 <1390936396-3962-3-git-send-email-jason.low2@hp.com>
 <20140128202334.GO9012@linux.vnet.ibm.com>
 <1390947041.2807.28.camel@j-VirtualBox>
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Sender: linux-kernel-owner@vger.kernel.org

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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