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Date: Sat, 23 Apr 2011 19:15:52 -0700
From: Andi Kleen <ak@linux.intel.com>
To: Stephane Eranian <eranian@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        arun@sharma-home.net, Arnaldo Carvalho de Melo <acme@infradead.org>,
        linux-kernel@vger.kernel.org, Lin Ming <ming.m.lin@intel.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, eranian@gmail.com,
        Arun Sharma <asharma@fb.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [generalized cache events] Re: [PATCH 1/1] perf tools: Add
 missing user space support for config1/config2
Message-ID: <20110424021552.GA3019@alboin.amr.corp.intel.com>
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> 
> That is what Andi is referring to. The issue causes bias and thus impacts
> the quality of the samples. On SNB, there is a new INST_RETIRED:PREC_DIST
> event. PREC_DIST=precise distribution. It tries to correct for the skid
> on this event on INST_RETIRED with PEBS (look at Vol3b).

Unfortunately even PDIST doesn't completely fix the problem, but
it only makes it somewhat better. Also it's only statistical,
so you won't get a guaranteed answer for every sample.

-Andi
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