linux-kernel - Re: [RFC][PATCH] perf, intel: Don't touch MSR_IA32

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Message-ID: <1347538265.15764.129.camel@twins>
Date:	Thu, 13 Sep 2012 14:11:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC][PATCH] perf, intel: Don't touch MSR_IA32_DEBUGCTLMSR from
 NMI context

On Thu, 2012-09-13 at 13:49 +0200, Stephane Eranian wrote:
> Should be, though it is pretty ugly to stash all of this in the
> put/get constraints.

Agreed, I almost added two extra functions for it but when I went to
look at where to call them I ended up next to get/put constraints.

> I will run some tests.
> 
> I wonder what this does when you come in to get/put with a fake cpuc. You don't
> want to perturb the local lbr which may be in use. 

Fake cpu will never set ->alloc and thus intel_pmu_has_lbr() should fail
and we don't do anything.
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