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

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Message-ID: <20130626120749.GH28407@twins.programming.kicks-ass.net>
Date:	Wed, 26 Jun 2013 14:07:49 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, 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>
> 
> 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

These patches are also done wrong; the first patches should add HSW
support for the existing features. Only then should you do patches for
new fail^wfeatures.
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