linux-kernel - Re: [PATCH 5/8] locking, mutex: Cancelable MCS lock for adaptive spinning

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Date:	Wed, 26 Feb 2014 09:45:25 -0800
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Waiman Long <waiman.long@...com>,
	mingo@...nel.org, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, tglx@...utronix.de, 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 5/8] locking, mutex: Cancelable MCS lock for adaptive
 spinning

On Wed, 2014-02-26 at 10:22 +0100, Peter Zijlstra wrote:
> On Tue, Feb 25, 2014 at 11:56:19AM -0800, Jason Low wrote:
> > On Mon, 2014-02-10 at 20:58 +0100, Peter Zijlstra wrote:
> > > +	for (;;) {
> > > +		if (prev->next == node &&
> > > +		    cmpxchg(&prev->next, node, NULL) == node)
> > > +			break;
> > > +
> > > +		/*
> > > +		 * We can only fail the cmpxchg() racing against an unlock(),
> > > +		 * in which case we should observe @node->locked becomming
> > > +		 * true.
> > > +		 */
> > > +		if (smp_load_acquire(&node->locked))
> > > +			return true;
> 
> I've stuck on in right about here. So that we don't unduly delay the
> cmpxchg() after the load of prev.

Ok.

Reviewed-by: Jason Low <jason.low2@...com>


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