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

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Message-ID: <CABPqkBRkE8z54a1gY00tmYkJ-4KHVv5XyLhvTCOUsDKVcQfP5w@mail.gmail.com>
Date:	Tue, 25 Jun 2013 14:40:58 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 0/7] perf, x86: Haswell LBR call stack support

On Tue, Jun 25, 2013 at 10:47 AM, Yan, Zheng <zheng.z.yan@...el.com> 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
>
I would also add that it does not work with leaf call optimizations:
A calls B, B calls C, C returns to A

and that can be fairly common with small functions.
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