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

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Message-ID: <CABPqkBSJu05YztcL435FH_rpcwWAi8czC9uUdiq3M0AjJ+_5Mg@mail.gmail.com>
Date:	Wed, 12 Sep 2012 20:00:54 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 Wed, Sep 12, 2012 at 7:45 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, 2012-09-12 at 19:37 +0200, Peter Zijlstra wrote:
>> Ah, so I do think EIO will re-enable LBR,
>
> OK, it does not, but the:
>
>>  also the handler is wrapped in
>> x86_pmu::{dis,en}able_all() which does end up calling
>> intel_pmu_lbr_{dis,en}able_all().
>
> Thing does the re-enable for us,
>

>>  However that leaves the MSR in the
>> exact same state on exit as it was on enter, so that's not a problem for
>> the: read-modify-write change.
>
> in a safe way.
Well, I think it does even when we have to stop events (x86_pmu_stop)
because the buffer is full. Looks like we always re-enable lbr. So looks
like the handler is a wash for debugctl.
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