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

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Date:	Fri, 19 Oct 2012 17:58:09 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	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 5:49 PM, Andi Kleen <ak@...ux.intel.com> wrote:
>> +     /*
>> +      * 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;
>> +     }
>
>
> Strictly you have to check for precise too, right?
>
Yes, the restriction is enforced only when PEBS is active and
this is what I do based on where pebs_aliases() is called.


> -Andi
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