linux-kernel - Re: [PATCH 8/5] llist: Remove cpu

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Message-ID: <1315853608.575.1.camel@twins>
Date:	Mon, 12 Sep 2011 20:53:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Huang Ying <ying.huang@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops

On Mon, 2011-09-12 at 18:38 +0200, Andi Kleen wrote:
> > so basically, in typical locking primitives (spinlock), it looks like
> > lower power consumption is preferred over getting the raw maximal
> 
> It's not only power, its:
> - Allow the other siblings make more progress on SMT
> - Do some backoff to stress the interconnect less (this is important on >2S):
> A tight loop which constantly writes is a extremly stressfull pattern.
> - Save some power by allowing the CPU to do more clock gating

If you're hitting a cmpxchg hard enough for any of those to make a
difference you're doing it wrong.
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