linux-kernel - Re: [PATCH 0/7] perf, x86: Haswell LBR call stack support

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Message-ID: <20130625153037.GA6123@two.firstfloor.org>
Date:	Tue, 25 Jun 2013 17:30:37 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	a.p.zijlstra@...llo.nl, eranian@...gle.com, andi@...stfloor.org
Subject: Re: [PATCH 0/7] perf, x86: Haswell LBR call stack support

On Tue, Jun 25, 2013 at 04:47:12PM +0800, Yan, Zheng wrote:
> From: "Yan, Zheng" <zheng.z.yan@...el.com>

Can you put this description somewhere in Documentation as a file?
(slightly extended, e.g. with the path name of the file to enable)

I think the users will later need this kind of context to use
the feature successfully.

-Andi

> 
> Haswell has a new feature that utilizes the existing Last Branch Record
> facility to record call chains. When the feature is enabled, function
> call will be collected as normal, but as return instructions are executed
> the last captured branch record is popped from the on-chip LBR registers.
> The LBR call stack facility can help perf to get call chains of progam
> without frame pointer. When perf tool requests PERF_SAMPLE_CALLCHAIN +
> PERF_SAMPLE_BRANCH_USER, this feature is dynamically enabled by default.
> This feature can be disabled/enabled through an attribute file in the cpu
> pmu sysfs directory.
> 
> The LBR call stack has following known limitations
>  1. Zero length calls are not filtered out by hardware
>  2. Exception handing such as setjmp/longjmp will have calls/returns not
>     match
>  3. Pushing different return address onto the stack will have calls/returns
>     not match
> 
> These patches are based upon tip/perf/core
> 
> Regards
> Yan, Zheng
> 

-- 
ak@...ux.intel.com -- Speaking for myself only.
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