netdev - Re: alignment faults in 3.6

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Message-ID: <20121012150045.GH5453@kvack.org>
Date:	Fri, 12 Oct 2012 11:00:45 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Måns Rullgård <mans@...sr.com>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	David Laight <David.Laight@...lab.com>, netdev@...r.kernel.org,
	Jon Masters <jonathan@...masters.org>
Subject: Re: alignment faults in 3.6

On Fri, Oct 12, 2012 at 04:48:20PM +0200, Eric Dumazet wrote:
> > Somehow, I doubt anyone would be willing to walk through all the noise the 
> > faults would likely trigger.
> 
> If this can be mapped to an event that can be used by perf tool, that
> might be useful ?

There are performance counters for the various different types of alignment 
faults supported by perf. Modern x86 makes the vast majority of unaligned 
accesses very low overhead -- the only ones that really hurt are those 
straddling different vm pages, but even those have little cost compared to 
obsolete microarchitectures (*cough* P4 *cough*).

		-ben
-- 
"Thought is the essence of where you are now."
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