linux-kernel - Re: [PATCH 07/12] perf_events: add LBR software filter support for Intel X86 (v2)

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Date:	Mon, 05 Dec 2011 23:29:40 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, acme@...hat.com,
	ming.m.lin@...el.com, andi@...stfloor.org, robert.richter@....com,
	ravitillo@....gov, will.deacon@....com, paulus@...ba.org,
	benh@...nel.crashing.org, rth@...ddle.net, ralf@...ux-mips.org,
	davem@...emloft.net, lethal@...ux-sh.org
Subject: Re: [PATCH 07/12] perf_events: add LBR software filter support for
 Intel X86 (v2)

On Fri, 2011-10-14 at 14:37 +0200, Stephane Eranian wrote:
> 
> This patch adds an internal sofware filter to complement
> the (optional) LBR hardware filter.
> 
> The software filter is necessary:
> - as a substitute when there is no HW LBR filter (e.g., Atom, Core)
> - to complement HW LBR filter in case of errata (e.g., Nehalem/Westmere)
> - to provide finer grain filtering (e.g., all processors)
> 
> Sometimes, the LBR HW filter cannot distinguish between two types
> of branches. For instance, to capture syscall as CALLS, it is necessary
> to enable the LBR_FAR filter which will also capture JMP instructions.
> Thus, a second pass is necessary to filter those out, this is what the
> SW filter can do.
> 
> The SW filter is built on top of the internal x86 disassembler. It
> is a best effort filter especially for user level code. It is subject
> to the availability of the text page of the program.
> 
> The SW filter is enabled on all Intel X86 processors. It is bypassed
> when the user is capturing all branches at all priv levels.

This patch is very seriously whitespace challenged. 
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