linux-kernel - Re: [PATCH 2/2] perf: SNB exclusive PMU access for INST_RETIRED:PREC

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Date:	Fri, 19 Oct 2012 18:45:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 2/2] perf: SNB exclusive PMU access for
 INST_RETIRED:PREC_DIST

On Fri, 2012-10-19 at 18:31 +0200, Stephane Eranian wrote:
> On Fri, Oct 19, 2012 at 6:27 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Fri, 2012-10-19 at 16:52 +0200, Stephane Eranian wrote:
> >> +static int intel_pebs_aliases_snb(struct perf_event *event)
> >> +{
> >> +       u64 cfg = event->hw.config;
> >> +       /*
> >> +        * for INST_RETIRED.PREC_DIST to work correctly with PEBS, it must
> >> +        * be measured alone on SNB (exclusive PMU access) as per Intel SDM.
> >> +        */
> >> +       if ((cfg & INTEL_ARCH_EVENT_MASK) == 0x01c0 && !event->attr.exclusive) {
> >> +               pr_info("perf: INST_RETIRED.PREC_DIST only works in exclusive mode\n");
> >> +               return -EINVAL;
> >
> > This isn't limited to admin, right? So the above turns into a DoS on the
> > console.
> >
> Ok, so how about a WARN_ON_ONCE() instead?

That should be fine I guess ;-)
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