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

[Jan Beulich <jbeulich@suse.com>]

On 14.09.2026 11:16, Juergen Gross wrote:
> On 26.08.26 06:57, Furkan Caliskan wrote:
>> --- 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.
> 
>> +            spin_unlock_irqrestore(&prv->lock, flags);
>> +            break;
>> +        }

Additionally please unlock first, then set rc. The compiler may do such a
rearrangement, but it also may not.

Jan