Re: [PATCH 2/5] xen/sched: rtds: enforce admission control in xl sched-rtds

[Jürgen Groß <jgross@xxxxxxxx>]

On 14.09.26 12:40, Furkan Çalışkan wrote:
> On 9/14/26 12:16, Juergen Gross wrote:
> > On 26.08.26 06:57, Furkan Caliskan wrote:
> > > Now that we have introduced admission control for new and
> > > removed units. Extend it to XEN_DOMCTL_SCHEDOP_putinfo and
> > > putvcpuinfo, so growing an existing reservation via
> > > xl sched-rtds is checked too.
> > >
> > > putinfo sets the same (period, budget) for every unit of a
> > > domain at once, so it tests the whole domain's utilization
> > > delta atomically, rather than unit-by-unit, which could
> > > spuriously reject an overall-acceptable change depending on
> > > iteration order.
> > >
> > > putvcpuinfo changes one unit at a time, so it just calls
> > > rt_admission_test() directly.
> > >
> > > Signed-off-by: Furkan Caliskan <frn1furkan10@xxxxxxxxx>
> > > ---
> > >    xen/common/sched/rt.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> > >    1 file changed, 42 insertions(+)
> > >
> > > diff --git a/xen/common/sched/rt.c b/xen/common/sched/rt.c
> > > index 9126320801..9643a277fe 100644
> > > --- a/xen/common/sched/rt.c
> > > +++ b/xen/common/sched/rt.c
> > > @@ -1527,11 +1527,43 @@ rt_dom_cntl(
> > >            op->u.rtds.budget = RTDS_DEFAULT_BUDGET / MICROSECS(1);
> > >            break;
> > >        case XEN_DOMCTL_SCHEDOP_putinfo:
> > > +    {
> > > +        uint64_t dom_old_util = 0, new_util, new_total;
> > > +        unsigned int nr_units = 0;
> > > +
> > >            rc = rt_validate_params(&op->u.rtds, &period, &budget);
> > >            if ( rc )
> > >                break;
> > >    +        new_util = rt_unit_utilization(period, budget);
> > > +
> > >            spin_lock_irqsave(&prv->lock, flags);
> > > +
> > > +        /*
> > > +         * Same (period, budget) for every unit of d: test and commit
> > > +         * the domain's whole utilization delta atomically, rather
> > > +         * than unit-by-unit, which could spuriously reject an
> > > +         * overall-acceptable change depending on iteration order.
> > > +         */
> > > +        for_each_sched_unit ( d, unit )
> > > +        {
> > > +            svc = rt_unit(unit);
> > > +            dom_old_util += rt_unit_utilization(svc->period, svc->budget);
> > > +            nr_units++;
> > > +        }
> > > +
> > > +        new_total = prv->utilization - dom_old_util +
> > > +                    (uint64_t)nr_units * new_util;
> > > +
> > > +        if ( new_total > prv->utilization && new_total > rt_utilization_cap(d) 
> > > )
> > > +        {
> > > +            rc = -EINVAL;
> > Is EINVAL a good choice here? I think a different error code might be wanted.
> Would EBUSY be okay here? Or what else would you suggest?
EBUSY is a liitle bit better. What do you think about ENOSPC?


Juergen

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