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[Xen-devel] Re: 0/4 Xen Scheduling Groups

I'm happy to see other folks interested in the concept of domain groups
because it relates to some of my work.  We seem to share many common
goals.  Particularly, we both made use of the hypervisor to support
groups of domains.  My first impressions:

Master/Slave Roles
While the master/slave model is certainly popular, it is not the only
relationship between domains.  Consider a groups of peers.  One way to
associate domains without an implicit hierarchy is to make groups a
first-class object, just like domains.  You can anchor scheduling
information against the group instead of on a single domain.  This
approach also has the benefit of allowing other projects to use group
information for more than scheduling.

Assuming I read your patches correctly, the intended use is that
administrators must remember which domains are masters and which are
members (and do so by domid).  Since it's easy to lose track of domids,
I suggest augmenting xm list and the supporting infrastructure to
provide cues to the administrator about group membership and roles.

Also, it would seem sched-group.c supports specification of members by
domid only.  Support for using domain names and uuids would be useful
because domids do change.

Assigning group names and group uuids quickly becomes essential too.
Imagine the chore of finding one member domain among many groups using
only the master's domid.  Reboots, migration, suspend/resume and
save/restore all change the domid, making it much more difficult.  This
leads me to my next questions...

What happens when any of the group members migrate?  Ditto for
suspend/resume and save/restore.  Automatically rebuilding groups after
these events is crucial.  So, it would be nice to see preservation of
the group association across the full lifecycle of domains.


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