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Re: [Xen-devel] Question to [PATCH 2 of 3] PoD: Allow pod_set_cache_targ

To: "Dietmar Hahn" <dietmar.hahn@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Question to [PATCH 2 of 3] PoD: Allow pod_set_cache_target hypercall to be preempted
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 15 Mar 2011 09:40:56 +0000
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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>>> On 15.03.11 at 10:00, Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx> wrote:
> I had a look at hypercall_create_continuation() and my understanding is that
> the caller on this cpu is prepared to start the hypercall again after
> getting scheduled next time and the hypercall is finished immediately to
> deliver irqs and events.
> But what about the other cpus in dom0? Are these waiting for an irq/event 
> from the cpu handling the long running hypercall?
> How do these benefit from this hypercall continuation?

One vCPU stuck in a long running hypercall can, depending on what
locks/mutexes/semaphores it holds, keep other vCPU-s in the same
domain from making progress. Whether that's what happens in
your case can only be determined by looking at what those other
vCPU-s were doing (or trying to do) at the time of the hang (from
SysRq-t or '0' [or 'd'] debug key output).


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