linux-kernel - Re: [PATCH V5 14/16] perf, x86: enable LBR callstack when recording callchain

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Message-ID: <20140924142110.GG2805@worktop.programming.kicks-ass.net>
Date:	Wed, 24 Sep 2014 16:21:10 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	kan.liang@...el.com
Cc:	eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
	paulus@...ba.org, acme@...nel.org, ak@...ux.intel.com,
	"Yan, Zheng" <zheng.z.yan@...el.com>
Subject: Re: [PATCH V5 14/16] perf, x86: enable LBR callstack when recording
 callchain

On Wed, Sep 10, 2014 at 10:09:11AM -0400, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> If a task specific event wants user space callchain but does not want
> branch stack sampling, enable the LBR call stack facility implicitly.
> The LBR call stack facility can help perf to get user space callchain
> in case of there is no frame pointer.
> 
> Note: this feature only affects how to get user callchain. The kernel
> callchain is always got by frame pointers.

Yeah, don't like this either. Suppose you have sane userspace (with
framepointers enabled) then you're now loosing the better option.
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