linux-kernel - Re: [PATCH 06/11] qspinlock: Optimize pending bit

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Message-ID: <53A17B15.3080904@redhat.com>
Date:	Wed, 18 Jun 2014 13:42:13 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, Waiman.Long@...com,
	tglx@...utronix.de, mingo@...nel.org
CC:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	paolo.bonzini@...il.com, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com, paulmck@...ux.vnet.ibm.com,
	riel@...hat.com, torvalds@...ux-foundation.org,
	raghavendra.kt@...ux.vnet.ibm.com, david.vrabel@...rix.com,
	oleg@...hat.com, gleb@...hat.com, scott.norton@...com,
	chegu_vinod@...com, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 06/11] qspinlock: Optimize pending bit

Il 15/06/2014 14:47, Peter Zijlstra ha scritto:
> XXX: merge into the pending bit patch..

Agree, or if not move it right after the pending bit patch, before the 
NR_CPUS optimization.

Paolo

> It is possible so observe the pending bit without the locked bit when
> the last owner has just released but the pending owner has not yet
> taken ownership.
>
> In this case we would normally queue -- because the pending bit is
> already taken. However, in this case the pending bit is guaranteed to
> be released 'soon', therefore wait for it and avoid queueing.
>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>

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