RE: [PATCH] perf_counter: Fix a race on perf_counter_ctx

[Metzger, Markus T]

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@xxxxxxx]
>Sent: Tuesday, August 18, 2009 4:00 PM
>To: Metzger, Markus T
>Cc: Peter Zijlstra; tglx@xxxxxxxxxxxxx; hpa@xxxxxxxxx; markus.t.metzger@xxxxxxxxx; linux-
>kernel@xxxxxxxxxxxxxxx; Paul Mackerras
>Subject: Re: [PATCH] perf_counter: Fix a race on perf_counter_ctx
>
>
>* Metzger, Markus T <markus.t.metzger@xxxxxxxxx> 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
>code?

The old BTS code used circular buffers.


regards,
markus.

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