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

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Message-ID: <20090615185907.GF6520@Krystal>
Date:	Mon, 15 Jun 2009 14:59:07 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, mingo@...hat.com,
	paulus@...ba.org, acme@...hat.com, linux-kernel@...r.kernel.org,
	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

* Peter Zijlstra (a.p.zijlstra@...llo.nl) wrote:
> On Mon, 2009-06-15 at 14:48 -0400, Mathieu Desnoyers wrote:
> > we should not care that much about the performance hit of
> > saving/restoring the cr2 register at each nmi entry/exit.
> 
> But we do, perf counters very much cares about nmi performance.
> 

To a point where it cannot afford a simple register save/restore ?

There is "caring" and "_caring_". I am tempted to ask what NMI handler
execution frequency you have in mind here to figure out if we are not
trying to optimize sub-nanoseconds per minutes. ;)

Mathieu


-- 
Mathieu Desnoyers
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