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

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] Question to [PATCH 2 of 3] PoD: Allow pod_set_cache_target hypercall to be preempted
From: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
Date: Tue, 15 Mar 2011 13:01:49 +0100
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Am 15.03.2011 schrieb "Jan Beulich <JBeulich@xxxxxxxxxx>":

> >>> 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).


> Jan


OK, thanks!



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