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Re: [Xen-devel] [PATCH v3 15/47] xen/sched: make rt scheduler vcpu agnostic.

On Sat, 2019-09-14 at 10:52 +0200, Juergen Gross wrote:
> Switch rt scheduler completely from vcpu to sched_unit usage.
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>

With just one additional note.

>   * This scheduler follows the Preemptive Global Earliest Deadline
> First (EDF)
>   * theory in real-time field.
> - * At any scheduling point, the VCPU with earlier deadline has
> higher priority.
> - * The scheduler always picks highest priority VCPU to run on a
> feasible PCPU.
> - * A PCPU is feasible if the VCPU can run on this PCPU and (the PCPU
> is idle or
> - * has a lower-priority VCPU running on it.)
> + * At any scheduling point, the UNIT with earlier deadline has
> higher priority.
From the real-time scheduling theory point of view, whether this really
makes sense (i.e., it still makes it possible to provide real-time
scheduling guarantees to guests, and if yes, how) has to be thought and

But this of course applies to the case when core-scheduling is actually
used, which is not (at least by default) for now. Moreover, we're
planning to make it possible to have it enabled on a per-pool basis,
which means it will be possible to have sched_rt cpupools with core
scheduling disabled.

On this grounds, I'm ok with the changes to this scheduler. When the
series is in, I'll add a note to this respect in some sched_rt related
piece of documentation.

Dario Faggioli, Ph.D
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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