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    SubjectRe: [patch 0/3] [Announcement] Performance Counters for Linux
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    From: Ingo Molnar <mingo@elte.hu>
    Date: Fri, 5 Dec 2008 07:10:12 +0100

    > * David Miller <davem@davemloft.net> wrote:
    >
    > > From: Thomas Gleixner <tglx@linutronix.de>
    > > Date: Thu, 04 Dec 2008 23:44:39 -0000
    > >
    > > > - No interaction with ptrace: any task (with sufficient permissions) can
    > > > monitor other tasks, without having to stop that task.
    > >
    > > This isn't going to work.
    > >
    > > If you look at the things the perfmon libraries do, you do need to stop
    > > the task.
    > >
    > > Consider counter virtualization as the most direct example. [...]
    >
    > Note that counter virtualization is not offered in the perfmon3 patchset
    > that has been posted to lkml. (It is part of the much larger 'full'
    > perfmon patchset which has not been submitted for integration)

    I know, it was yanked out to make a merge more likely.

    > Relying on ptrace machinery can be considered one of the bigger design
    > mistakes of the permon3 patchset.

    I totally disagree.

    > We pointed that out in review, and now we demonstrate it via this
    > patchset that it can be done much cleaner and much simpler. (Please stay
    > tuned for -v2 if you want to see the proof of the pudding.)

    I hope it will provide enough for full PAPI library support, otherwise
    it's useless for most of the world.


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