RE: [PATCH] Kick CPUS that might be sleeping in cpus_idle_wait

[Pallipadi, Venkatesh]

>-----Original Message-----
>From: linux-kernel-owner@xxxxxxxxxxxxxxx 
>[mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Steven Rostedt
>Sent: Thursday, January 10, 2008 6:44 AM
>To: Ingo Molnar
>Cc: LKML; Linus Torvalds; Andrew Morton; Thomas Gleixner; 
>Brown, Len; Pallipadi, Venkatesh; Adam Belay; Peter Zijlstra; 
>Andi Kleen
>Subject: Re: [PATCH] Kick CPUS that might be sleeping in cpus_idle_wait
>
>
>
>On Thu, 10 Jan 2008, Ingo Molnar wrote:
>> > FYI, I just hit this hang on 2.6.24-rc6 without any extra 
>patches. So,
>> > unless 2.6.24-rc7 did anything to fix this issue, this is a high
>> > priority bug (IMHO).
>>
>> i'm wondering why this only triggered now. Is this something new in
>> 2.6.24?
>
>It only triggeres with the switching of the idle governors. 
>And not just
>one, you need to switch twice. The first loading of a governor does not
>call cpu_idle_wait, but the second one does. NO_HZ must also 
>be enabled,
>plus this needs to happen when no events or threads are 
>scheduled to run
>on a CPU, which limits this to boot up.
>
>Also, this only seems to happen on my 2x2 (4way) and only once 
>in a while.
>
>I'm surprised that I'm the only one so far to report it. I can 
>boot up the
>2.6.23 kernel on this box to see if it also hangs sometimes. But, as I
>said, it may take several hundreds of tries to see it.


With 2.6.23, you can try compiling acpi processor.ko as a module and
doing insmod and rmmod in a loop. That should call cpu_idle_wait very
frequently.

Thanks,
Venki
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