RE: [Xen-devel] cpuidle causing Dom0 soft lockups

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Juergen Gross [mailto:juergen.gross@xxxxxxxxxxxxxx] 
>Sent: 2010年2月3日 20:19
>
>Tian, Kevin wrote:
>>> From: Jan Beulich
>>> Sent: 2010年2月3日 18:16
>>>
>>>>>> "Yu, Ke" <ke.yu@xxxxxxxxx> 02.02.10 18:07 >>>
>>>>> Just fyi, we now also have seen an issue on a 24-CPU 
>system that went
>>>>> away with cpuidle=0 (and static analysis of the hang 
>hinted in that
>>>>> direction). All I can judge so far is that this likely has 
>>> something to do
>>>>> with our kernel's intensive use of the poll hypercall (i.e. 
>>> we see vCPU-s
>>>>> not waking up from the call despite there being pending 
>unmasked or
>>>>> polled for events).
>>>> We just identified the cause of this issue, and is trying to 
>>> find appropriate way to fix it.
>>>
>>> Hmm, while I agree that the scenario you describe can be a 
>problem, I
>>> don't think it can explain the behavior on the 24-CPU system pointed
>>> out above, nor the one Juergen Gross pointed out yesterday.
>> 
>> Is 24-CPU system observed with same likelihood as 64-CPU system to
>> hang at boot time, or less frequent? Ke just did some 
>theoretical analysis
>> by assuming some values. There could be other factors added 
>to latency
>> and each system may have different characteristics too. We can't
>> draw conclusion whether smaller system will face same issue, 
>by simply
>> changing CPU number in Ke's formula. :-) Possibly you can 
>provide cpuidle
>> information on your 24-core system for further comparison.
>
>My 4-core system hangs _always_. For minutes. If I press any key on the
>console it will resume booting with soft lockup messages (all cpus were
>in xen_safe_halt).
>Sometimes another hang occurs, sometimes the system will come 
>up without
>further hangs.
>
>Juergen
>

interesting. Then did you also observe hang disappeared by disabling
cpuidle? Your case really looks like some missed event scenario, in
which key press just kicks cpu alive...

Thanks,
Kevin

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