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

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

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

-- 
Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technolgy Solutions               e-mail: juergen.gross@xxxxxxxxxxxxxx
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