linux-kernel - Re: [RFC][PATCH 10/11] perf, x86: use LBR for PEBS IP+1 fixup

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Date:	Thu, 04 Mar 2010 09:57:26 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, paulus@...ba.org,
	robert.richter@....com, fweisbec@...il.com
Subject: Re: [RFC][PATCH 10/11] perf, x86: use LBR for PEBS IP+1 fixup

On Wed, 2010-03-03 at 22:50 +0100, Stephane Eranian wrote:

> I think systematically and transparently using LBR to correct PEBS off-by-one
> problem is not such a good idea. You've basically highjacked LBR and user
> cannot use it in a different way.

Well, they could, it just makes scheduling the stuff more interesting.

> There are PEBS+LBR measurements where you care about extracting the LBR data.
> There are PEBS measurements where you don't care about getting the correct IP.
> I don't necessarily want to pay the price, especially when this could
> be done offline in the tool.

There are some people who argue that fixing up that +1 insn issue is
critical, sadly they don't appear to want to argue their case in public.
What we can do is make it optional I guess.

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