linux-kernel - Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

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Message-ID: <20090615184714.GI11248@elte.hu>
Date:	Mon, 15 Jun 2009 20:47:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, mingo@...hat.com,
	hpa@...or.com, paulus@...ba.org, acme@...hat.com,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	penberg@...helsinki.fi, vegard.nossum@...il.com, efault@....de,
	jeremy@...p.org, npiggin@...e.de, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain
	support to use NMI-safe methods


* Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:

> > If it's a slowdown then the decision is easy: we dont want this, 
> > we want to push the overhead into the sampling code, away from 
> > common codepaths.
> 
> I did not try to make the "hand unroll + ret" the default. I 
> therefore don't know if it is faster or slower than iret. But I 
> prefered to stay on the safe side and only modify the exceptions 
> nested within NMI handlers.

hm, i misread that bit then. Too bad.

Btw., that speedup question is still valid. (Just not relevant here 
and now.)

	Ingo
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