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

[Metzger, Markus T]

>-----Original Message-----
>From: Metzger, Markus T
>Sent: Tuesday, August 18, 2009 4:15 PM
>To: Ingo Molnar
>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
>
>>-----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.

Ingo,

I'm not making any progress with the kernel hang.

User-mode tracing is working OK (e.g. -e branches:u) and circular buffers are
working fine, as well. I can do "perf top -c 1 -e branches:u" and simultaneous
"perf record -c 1 -e branches:u", but as soon as I try to trace the kernel,
it hangs (and /var/log/messages is typically garbled).

Please drop the BTS patch.

thanks and regards,
markus.

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