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RE: [Xen-devel] [PATCH] Fix softlockup issue after vcpu hotplug

  • To: "Graham, Simon" <Simon.Graham@xxxxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
  • Date: Fri, 2 Feb 2007 12:36:47 +0800
  • Delivery-date: Thu, 01 Feb 2007 20:36:28 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-topic: [Xen-devel] [PATCH] Fix softlockup issue after vcpu hotplug

>From: Graham, Simon [mailto:Simon.Graham@xxxxxxxxxxx]
>Sent: 2007年2月2日 11:47
>> The only theoretical problem with this approach is if you got time
>> stolen
>> that accumulated to more than five seconds, but this happened in two
>> more
>> bursts, back-to-back. Then no one stolen period would be enough to
>> trigger
>> the touch, but also the guest may not be running for long enough to
>> schedule
>> the softlockup thread. I really don't believe this would be an issue
>> ever in
>> practise however, given sane scheduling parameters and load on the
>> system.
>> If the system were loaded/configured so it could happen, the guest
>> would be
>> in dire straits for other reasons.
>How about using a slightly smaller value like 1 or 2 s -- something
>larger than the expected wakeup latency etc but small enough that it
>would take multiple back-to-back bursts to hit 10s...

If you really concern this value, how about make it configurable with 
a default value? Or even a boot option? Smaller the value is, the effect 
of watchdog thread to check weird behavior is wakened. On the 
contrary, bigger value enlarges possibility of accumulated stolen time. 
However for now, anyway we have no concrete example to prove 
how frequent back-to-back bursts may happen and whether 
accumulated case does happen. Most likely that may happen in 
some heavy loaded system with many vcpus. But in that case, maybe 
scalability issue on other areas will jump out first. :-)


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