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

From: Peter Zijlstra
Date: Wed Sep 24 2014 - 10:21:24 EST

On Wed, Sep 10, 2014 at 10:09:11AM -0400, kan.liang@xxxxxxxxx wrote:
> From: Kan Liang <kan.liang@xxxxxxxxx>
> 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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