linux-kernel - Re: [PATCH v8 12/14] x86: perf: intel

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Message-ID: <87oaq4nqco.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Mon, 12 Jan 2015 14:19:35 +0200
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, markus.t.metzger@...el.com,
	mathieu.poirier@...aro.org, acme@...radead.org
Subject: Re: [PATCH v8 12/14] x86: perf: intel_pt: Intel PT PMU driver

Peter Zijlstra <peterz@...radead.org> writes:

> On Fri, Nov 14, 2014 at 03:43:45PM +0200, Alexander Shishkin wrote:
>> +static void pt_event_stop(struct perf_event *event, int mode)
>> +{
>> +	struct pt *pt = this_cpu_ptr(&pt_ctx);
>> +
>> +	ACCESS_ONCE(pt->handle_nmi) = 0;
>
> Why is this needed? Will the hardware still generate interrupts if you
> stop the PT thing?

It's meant to serialize nmi handler against the pmu:: callbacks, but now
you mentioned it, it looks very much redundant.

Cheers,
--
Alex
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