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Re: [Xen-devel] [PATCH 0 of 3] Remus: control tool

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0 of 3] Remus: control tool
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 02 Dec 2009 18:25:29 +0000
Cc: "andy@xxxxxxxxx" <andy@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "konrad.wilk@xxxxxxxxxx" <konrad.wilk@xxxxxxxxxx>
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On 02/12/2009 18:17, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

> On 12/02/09 00:07, Keir Fraser wrote:
>> The issue in 2.6.18 was that, if doing back-to-back save/restores, the next
>> event-channel notification could come in before domU was finished with
>> previous s/r cycle, and then the notification got dropped. There are a
>> number of ways of dealing with that of course: I implemented a little state
>> machine; or you could probably do it with some kind of ticket-based scheme;
>> or perhaps have the evtchn irq handler spawn a kthread which blocks on the
>> mutex (I liked that one least as it needs to allocate resources).
> Hm, my first thought is "why does that matter?".  But I guess the
> host/guest save protocol is fairly brittle, and if the guest doesn't
> respond to a particular save it will get wedged.  But then, should the
> control stack be sending back to back save requests?  Shouldn't it wait
> until the previous save has finished?

>From the tools p.o.v. the restore has finished when it kicks off execution
of the guest. It's not that hard to handle this in the guest; you just need
to do it. ;-)

 -- Keir

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