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Message-ID: <20090615182828.GE11248@elte.hu>
Date: Mon, 15 Jun 2009 20:28:28 +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
* Ingo Molnar <mingo@...e.hu> wrote:
> The GUP based method is pretty generic though - and can be used on
> other architectures as well. It's not as fast as direct access
> though.
Another question is: your patch switches over all normal exceptions
from IRET to hand-unroll+RET.
It would be really nice to benchmark it (via 'perf stat' for example
;-) whether that's a slowdown or a speedup.
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.
[ If on the other hand it's a speedup of a few cycles then we have
the problem of me suddenly liking this patch a whole lot more ;-) ]
Ingo
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