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    SubjectRE: [PATCH] perf_counter: Fix a race on perf_counter_ctx
    >-----Original Message-----
    >From: Ingo Molnar []
    >Sent: Tuesday, August 18, 2009 4:00 PM
    >To: Metzger, Markus T
    >Cc: Peter Zijlstra;;;; linux-
    >; Paul Mackerras
    >Subject: Re: [PATCH] perf_counter: Fix a race on perf_counter_ctx
    >* Metzger, Markus T <> wrote:
    >> Well, that would push out the limit a bit, but it would still be
    >> quite fragile.
    >> Currently, I'm not sure that this (i.e. that the interrupt
    >> handling takes too long) is the underlying problem of the hangs
    >> that I'm seeing.
    >I havent seen a plausible theory yet about why an actual lockup
    >would happen on your box.

    So you do not think that taking too long in the ISR could cause this?

    And is it working on your box?

    >Does the timer IRQ perhaps slow down to such a degree that it can
    >never make progress and gets re-triggered again and again? We saw
    >such things with the function tracer.

    How would I test this?

    >Did the sampling of kernel-mode tasks ever work with the old BTS

    The old BTS code used circular buffers.


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