Re: [Xen-devel] Design session report: Live-Updating Xen

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Juergen 
> Gross
> Sent: 18 July 2019 10:00
> To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Sarah Newman <srn@xxxxxxxxx>; 
> Foerster, Leonard
> <foersleo@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Design session report: Live-Updating Xen
> 
> On 17.07.19 00:27, Andrew Cooper wrote:
> > On 16/07/2019 05:20, Sarah Newman wrote:
> >> On 7/15/19 8:48 PM, Juergen Gross wrote:
> >>> On 15.07.19 21:31, Sarah Newman wrote:
> >>>> On 7/15/19 11:57 AM, Foerster, Leonard wrote:
> >>>> ...
> >>>>> A key cornerstone for Live-update is guest transparent live migration
> >>>> ...
> >>>>>      -> for live migration: domid is a problem in this case
> >>>>>          -> randomize and pray does not work on smaller fleets
> >>>>>          -> this is not a problem for live-update
> >>>>>          -> BUT: as a community we shoudl make this restriction go away
> >>>>
> >>>> Andrew Cooper pointed out to me that manually assigning domain IDs
> >>>> is supported in much of the code already. If guest transparent live
> >>>> migration gets merged, we'll look at passing in a domain ID to xl,
> >>>> which would be good enough for us. I don't know about the other
> >>>> toolstacks.
> >>>
> >>> The main problem is the case where on the target host the domid of the
> >>> migrated domain is already in use by another domain. So you either need
> >>> a domid allocator spanning all hosts or the change of domid during
> >>> migration must be hidden from the guest for guest transparent migration.
> >>
> >> Yes. There are some cluster management systems which use xl rather
> >> than xapi.
> >> They could be extended to manage domain IDs if it's too difficult to
> >> allow
> >> the domain ID to change during migration.
> >
> > For a v1 feature, having a restriction of "you must manage domids across
> > the cluster" is a fine.  Guest-transparent migration is a very important
> > feature, and one where we are lacking in relation to other hypervisors.
> >
> > Longer term, we as the Xen community need to figure out a way to remove
> > the dependency on domids, at which point the cluster-wide management
> > restriction can be dropped.  This isn't going to be a trivial task, but
> > it will be a worthwhile one.
> 
> Another problem are Xenstore watches. With guest transparent LM they are
> lost today as there is currently no way to migrate them to the target
> Xenstore.
> 
> Live-Update could work around this issue via Xenstore-stubdom.

Watches are one problem. There's also the problem of pending transactions.

  Paul

> 
> 
> Juergen
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxxx
> https://lists.xenproject.org/mailman/listinfo/xen-devel
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel