linux-kernel - Re: [PATCH] arch/arm/kernel: use cpu

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Date:	Wed, 15 Dec 2010 00:00:01 +0100
From:	Jonathan Neuschäfer <j.neuschaefer@....net>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Jonathan Neuschäfer <j.neuschaefer@....net>,
	linux-kernel@...r.kernel.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Tony Lindgren <tony@...mide.com>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Eric Miao <eric.y.miao@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arch/arm/kernel: use cpu_relax() in halt loops

On Tue, Dec 14, 2010 at 10:51:26PM +0000, Russell King - ARM Linux wrote:
> On Tue, Dec 14, 2010 at 11:48:48PM +0100, Jonathan Neuschäfer wrote:
> > Looking throught arch/arm/kernel/ I found some halt loops.
> > I just thought we could save some power here using cpu_relax(),
> > or am I missing something?
> 
> #if __LINUX_ARM_ARCH__ == 6
> #define cpu_relax()                     smp_mb()
> #else
> #define cpu_relax()                     barrier()
> #endif
> 
> IOW, it's either a memory barrier or compiler barrier on ARM; it
> doesn't do any power saving.

Okay, thanks for that explanation.
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