linux-kernel - Re: [PATCH V3 1/3] perf tools: enable LBR call stack support

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Message-ID: <87ppclqcif.fsf@sejong.aot.lge.com>
Date:	Tue, 18 Nov 2014 14:54:48 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	kan.liang@...el.com
Cc:	acme@...nel.org, jolsa@...hat.com, a.p.zijlstra@...llo.nl,
	eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
	paulus@...ba.org, ak@...ux.intel.com
Subject: Re: [PATCH V3 1/3] perf tools: enable LBR call stack support

On Fri, 14 Nov 2014 08:44:10 -0500, kan liang wrote:
> From: Kan Liang <kan.liang@...el.com>
>
> Currently, there are two call chain recording options, fp and dwarf.
> Haswell has a new feature that utilizes the existing LBR facility to
> record call chains. So it provides the third options to record call
> chain. This patch enables the lbr call stack support.
>
> LBR call stack has some limitations. It reuses current LBR facility, so
> LBR call stack and branch record can not be enabled at the same time. It
> is only available for user callchain.
> However, LBR call stack can work on the user app which doesn't have
> frame-pointer or dwarf debug info compiled. It is a good alternative
> when nothing else works.

So this is only for Haswell or later, right?  What if user gives it to
the other CPUs - is it fail or ignore silently?  I think we need to warn
user about it more kindly..

Thanks,
Namhyung
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