linux-kernel - Re: [PATCH V2 6/7] perf, x86: Use LBR call stack to get user callchain

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Message-ID: <20121024123124.GU2095@tassilo.jf.intel.com>
Date:	Wed, 24 Oct 2012 05:31:24 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	"Yan, Zheng" <zheng.z.yan@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH V2 6/7] perf, x86: Use LBR call stack to get user
 callchain

On Wed, Oct 24, 2012 at 02:21:43PM +0200, Stephane Eranian wrote:
> But still, if I do:
> $  perf record -g -e cpu/cycles/k ........
> 
> Looks like your code will activate LBR cstack for user stack even
> though I don't use it.
> I know it won't generate any user samples (theoretically) but you are
> still commandeering
> the LBR resource which other events may want to use.

You can disable it in sysfs. LBR is a power user feature and they will
know how to do this.

See it as a "prefer the needs of the 95+% over the needs of the few" default

-Andi
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