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

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Message-ID: <CABPqkBQ5kCyGByFS-D62RYg2VUf_W-rJKDH=AzyrcaBPVY-eFQ@mail.gmail.com>
Date:	Fri, 19 Oct 2012 18:31:12 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
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, 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?
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