Re: [Xen-devel] [RFC] Extend the number of event channels availabe to guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.09.12 at 09:55, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Thu, 2012-09-20 at 08:47 +0100, Jan Beulich wrote:
>> One aspect to also consider is migration - will the guest have to
>> re-issue the extending hypercall, or will this be taken care of for
>> it? If the former approach is chosen, would the guest be
>> expected to deal with not being able to set up the extension
>> again on the new host? 
> 
> We only properly care about N->N and N->N+1 migrations, if we think that
> we would never reduce the limit over a hypervisor version upgrade then
> this would be fine, I think.
> 
> We do a similar thing with the grant table v2 stuff I think, i.e. panic
> after migration if we can't setup the feature again.

Which doesn't sound right - if hypervisor/tools did the re-setup,
then migration could fail in a recoverable way (i.e. continuing to
run on the old host) instead. After all, this may not be just about
feature availability but - especially if indeed there were multiple
pages to be allocated by the hypervisor - resource constraints.

Jan


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