From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Eranian <eranian@google.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Oleg Nesterov <oleg@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFC][PATCH] perf, intel: Don't touch MSR_IA32_DEBUGCTLMSR from NMI context
Date: Wed, 12 Sep 2012 19:37:26 +0200 [thread overview]
Message-ID: <1347471446.15764.67.camel@twins> (raw)
In-Reply-To: <CABPqkBQsJr_Cp36Df-etOaHhGh8T6XVngraDQt52ZtKahr6KBQ@mail.gmail.com>
On Wed, 2012-09-12 at 18:42 +0200, Stephane Eranian wrote:
> We use FREEZE_LBR_ON_PMI to sync LBR data with counter overflows.
> That means, LBR is already frozen by the time we get to the handler. But
> that means we need to re-enable LBR when we leave the handler. I don't
> think EOI is going to magically re-enable it. So we need to touch DEBUGCTL
> in the irq handler.
Ah, so I do think EIO will re-enable LBR, also the handler is wrapped in
x86_pmu::{dis,en}able_all() which does end up calling
intel_pmu_lbr_{dis,en}able_all(). 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.
Its just that the x86_pmu::disable() for the throttle could leave the
MSR in a different state on exit than it entered with. This patch avoids
that.
next prev parent reply other threads:[~2012-09-12 17:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-12 16:22 [RFC][PATCH] perf, intel: Don't touch MSR_IA32_DEBUGCTLMSR from NMI context Peter Zijlstra
2012-09-12 16:42 ` Stephane Eranian
2012-09-12 17:37 ` Peter Zijlstra [this message]
2012-09-12 17:45 ` Peter Zijlstra
2012-09-12 18:00 ` Stephane Eranian
2012-09-12 18:17 ` Peter Zijlstra
2012-09-12 18:50 ` Stephane Eranian
2012-09-12 18:52 ` Peter Zijlstra
2012-09-12 19:00 ` Stephane Eranian
2012-09-12 17:36 ` Oleg Nesterov
2012-09-12 17:41 ` Peter Zijlstra
2012-09-13 10:23 ` Peter Zijlstra
2012-09-13 11:49 ` Stephane Eranian
2012-09-13 12:11 ` Peter Zijlstra
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