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Date: Wed, 17 Dec 2008 08:34:07 +0100
From: "stephane eranian" <eranian@googlemail.com>
Reply-To: eranian@gmail.com
To: "Paul Mackerras" <paulus@samba.org>
Subject: Re: [patch] Performance Counters for Linux, v4
Cc: "Peter Zijlstra" <a.p.zijlstra@chello.nl>, "Ingo Molnar" <mingo@elte.hu>,
        linux-kernel@vger.kernel.org, "Thomas Gleixner" <tglx@linutronix.de>,
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        "Eric Dumazet" <dada1@cosmosbay.com>,
        "Robert Richter" <robert.richter@amd.com>,
        "Arjan van de Ven" <arjan@infradead.org>,
        "Peter Anvin" <hpa@zytor.com>, "David S. Miller" <davem@davemloft.net>,
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Paul,

On Wed, Dec 17, 2008 at 12:06 AM, Paul Mackerras <paulus@samba.org> wrote:
>
> I think we need a "full-time" attribute for counters and groups that
> says "I need to be on the whole time", where "whole time" means
> whenever the task is running, for a per-task counter or group, or
> continuously for per-cpu counters/groups.
>
Who would want not to be the only owner of the PMU?

Especially when you know that if you don't, you may be sharing it
with another user who may perturb your measurement, for instance
because of heavy sampling while you are just counting. It is a tradeoff
between flexibility and accuracy. Which one is more important?