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

To: "Graham, Simon" <Simon.Graham@xxxxxxxxxxx>, "Tian, Kevin" <kevin.tian@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Fix softlockup issue after vcpu hotplug
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Thu, 01 Feb 2007 18:24:35 +0000
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On 1/2/07 14:31, "Graham, Simon" <Simon.Graham@xxxxxxxxxxx> wrote:

> 3. I actually saw a bunch of cases where there was a mongo stolen value
> during apparently normal
>    operation (in the ones I've looked at, the system as a whole was not
> particularly stressed); I
>    need to work on exactly why the domain is not being secheduled, but
> in the meantime, shouldn't
>    this patch stop the incorrect soft lockup in DomU when the hypervisor
> fails to schedule the
>    domain for a long period? (not exactly related to VCPU hotplug I
> know)

No, the patch that Kevin provided cannot work because it touches the
watchdog before jiffies has been updated. Since both jiffy update and
watchdog check happens inside do_timer(), this is a hard problem to fix for
Linux 2.6.16. You could push the watchdog touch inside the following loop
that calls do_timer(): I think that would work!

 -- Keir



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