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

[Andi Kleen <andi@firstfloor.org>]

On Tue, Jun 25, 2013 at 04:47:12PM +0800, Yan, Zheng wrote:
> From: "Yan, Zheng" <zheng.z.yan@intel.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@linux.intel.com -- Speaking for myself only.