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Re: [Xen-devel] Re: Scheduling groups, credit scheduler support



First let me restate that this is a great use for groups.

The patches use the term master and member, but it is more of a peer
relationship only effecting scheduler accounting. The significance of
the "master" is that the "member" domains inherit the master's cpu
weight and credits are charged to the master. The master doesn't exert
any explicit control over its group members (although there may be a
use case for doing so). This is the specific functionality we need for
stub domains, where the credits consumed by a stub domain need to be
charged to the HVM guest domain.

A primary concern is that the approach potentially precludes the use of VMM-based grouping information in other situations where groups are useful because the group abstraction exists only in the scheduler.

Also, even though it's currently just used for accounting, group membership information is effectively attached to a single domain. Assuming I've read correctly, when the master domain goes away, so does the membership information. That's probably OK for HVM stub domains, but what if the domains are peers as in the dom0 disaggregation case or (thinking even further ahead) in the general domain decomposition case?

One way to avoid both concerns is to create and manage group-tracking objects independently of domain-tracking objects. In other words, make groups a first-class object. They could be referenced by schedulers as well as any other parts of the VMM that want to make use of group information.

Regards,
Chris

P.S. - A refresh of my previous group implementation is coming RSN. I'm testing to make sure it still works as intended.
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