Re: [Xen-devel] [PATCH v3 30/47] xen/sched: add support for multiple vcpus per sched unit where missing

[Jürgen Groß <jgross@xxxxxxxx>]

On 24.09.19 17:22, Jan Beulich wrote:
> On 24.09.2019 17:09, Jürgen Groß wrote:
> > On 24.09.19 17:00, Jan Beulich wrote:
> > > On 24.09.2019 16:41, Jürgen Groß wrote:
> > > > for_each_sched_unit_vcpu() for an idle
> > > > unit might end premature when one of the vcpus is running in another
> > > > unit (idle_vcpu->sched_unit != idle_unit).
> > > Oh, that (v)->sched_unit == (i) in the construct is clearly unexpected.
> > > Is this really still needed by the end of the series? I realize that
> > > _some_ check is needed, but could this perhaps be arranged in a way
> > > that you'd still hit all vCPU-s when using it on an idle unit, no
> > > matter whether they're in use as a substitute in a "real" unit?
> > I could do that by having another linked list in struct vcpu. This way
> > I can avoid it.
> Oh, no, not another list just for this purpose. I was rather thinking
> of e.g. a comparison of IDs.
That would result either in something like:

(v)->vcpu_id < (u)->unit_id + (u)->res->cpupool->granularity

requiring to make struct sched_resource public as keyhandler.c needs
for_each_sched_unit_vcpu() plus being quite expensive, or:

!(u)->next_in_list || (v)->vcpu_id < (u)->next_in_list->unit_id

which seems to be more expensive as the current variant, too.


Juergen


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