linux-kernel - Re: [RFC PATCH 2/3 v2] perf: Implement Nehalem uncore pmu

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Message-ID: <AANLkTimb_DR+c7BJMdN4QgdT_7WwRMixQGXaOFEwqDDt@mail.gmail.com>
Date:	Thu, 25 Nov 2010 22:10:02 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Lin Ming <ming.m.lin@...el.com>, Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC PATCH 2/3 v2] perf: Implement Nehalem uncore pmu

On Thu, Nov 25, 2010 at 7:20 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> Yep, I see no reason to dis-allow sampling. Sure its hard to make sense
>> of it, but since there are people who offline all but one cpu of a
>> package,
>
> Assuming they don't have any active PCI devices either.
>
Good point.

>> I bet there are people who will run just one task on a package
>> as well.
>
> In that case the sampling has a 1/NUM-CPU-THREADS-IN-PACKAGE chance
> to report the right task (or actually somewhat less because the measurement
> skew for uncore is much higher than for normal events)
>
> Really for per core measurements using the OFFCORE events is much better.
>
yes, OFFCORE_RESPONSE is much more useful.
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