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From: Andi Kleen <andi@firstfloor.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Huang Ying <ying.huang@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, Andi Kleen <andi@firstfloor.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops
Date: Mon, 12 Sep 2011 16:23:05 +0200	[thread overview]
Message-ID: <20110912142305.GN7761@one.firstfloor.org> (raw)
In-Reply-To: <1315836358.26517.43.camel@twins>

On Mon, Sep 12, 2011 at 04:05:58PM +0200, Peter Zijlstra wrote:
> Subject: llist: Remove cpu_relax() usage in cmpxchg loops
> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date: Mon Sep 12 15:50:49 CEST 2011
> 
> Initial benchmarks show they're a net loss (2 socket wsm):
> 

May still save power. however:

>  		entry = cmpxchg(&head->first, old_entry, new);
>  		if (entry == old_entry)
>  			break;
> -		cpu_relax();

You need at least a barrier() then, otherwise the compiler could
change the memory order in the loop.

-Andi

  reply	other threads:[~2011-09-12 14:23 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-08  6:00 [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 1/5] llist, Make all llist functions inline Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 2/5] llist, Define macro to check NMI safe cmpxchg Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 3/5] llist, Move cpu_relax after cmpxchg Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 4/5] llist, Return whether list is empty before adding in llist_add Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 5/5] irq_work, Use llist in irq_work Huang Ying
2011-09-12 14:05 ` [PATCH 6/5] llist: Add llist_next() Peter Zijlstra
2011-09-12 14:05 ` [PATCH 7/5] sched: Convert to use llist Peter Zijlstra
2011-09-12 14:05 ` [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops Peter Zijlstra
2011-09-12 14:23   ` Andi Kleen [this message]
2011-09-12 14:23     ` Peter Zijlstra
2011-09-12 14:47     ` Mathieu Desnoyers
2011-09-12 15:09       ` Peter Zijlstra
2011-09-12 15:24       ` Peter Zijlstra
2011-09-12 16:38       ` Andi Kleen
2011-09-12 18:53         ` Peter Zijlstra
2011-09-12 14:26   ` Avi Kivity
2011-09-12 14:32     ` Peter Zijlstra
2011-09-13 11:43       ` Avi Kivity
2011-09-13 14:22         ` Peter Zijlstra
2011-09-13 14:51           ` Avi Kivity
2011-09-13 14:53             ` Peter Zijlstra
2011-09-12 14:06 ` [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Peter Zijlstra

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