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


  • To: Sarah Newman <srn@xxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, "Foerster, Leonard" <foersleo@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 16 Jul 2019 23:27:48 +0100
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  • Delivery-date: Tue, 16 Jul 2019 22:28:02 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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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.

~Andrew

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