Re: [Xen-devel] [PATCH v6 for Xen 4.7 1/4] xen: enable per-VCPU parameter settings for RTDS scheduler

[Chong Li <lichong659@xxxxxxxxx>]

On Mon, Mar 7, 2016 at 11:53 AM, Dario Faggioli
<dario.faggioli@xxxxxxxxxx> wrote:
> On Mon, 2016-03-07 at 09:40 -0700, Jan Beulich wrote:
>> > > > On 07.03.16 at 17:28, <lichong659@xxxxxxxxx> wrote:
>> > On Mon, Mar 7, 2016 at 6:59 AM, Jan Beulich <JBeulich@xxxxxxxx>
>> > wrote:
>> > >
>> > > > @@ -1163,6 +1173,96 @@ rt_dom_cntl(
>> > > >
>> > > > +    case XEN_DOMCTL_SCHEDOP_getvcpuinfo:
>> > > > +        if ( guest_handle_is_null(op->u.v.vcpus) )
>> > > > +        {
>> > > > +            rc = -EINVAL;

>
>> > > > +            {
>> > > > +                rc = -EINVAL;
>> > > > +                break;
>> > > > +            }
>> > > > +
>> > > > +            spin_lock_irqsave(&prv->lock, flags);
>> > > > +            svc = rt_vcpu(d->vcpu[local_sched.vcpuid]);
>> > > > +            local_sched.s.rtds.budget = svc->budget /
>> > > > MICROSECS(1);
>> > > > +            local_sched.s.rtds.period = svc->period /
>> > > > MICROSECS(1);
>> > > > +            spin_unlock_irqrestore(&prv->lock, flags);
>> > > > +
>> > > > +            if ( __copy_to_guest_offset(op->u.v.vcpus, index,
>> > > > +                    &local_sched, 1) )
>> > > > +            {
>> > > > +                rc = -EFAULT;
>> > > > +                break;
>> > > > +            }
>> > > > +            if ( (++index > 0x3f) && hypercall_preempt_check()
>> > > > )
>> > > > +                break;

>
>> > > > +        }
>> > > > +
>> > > > +        if ( !rc && (op->u.v.nr_vcpus != index) )
>> > > > +            op->u.v.nr_vcpus = index;
>> > > I don't think the right side of the && is really necessary /
>> > > useful.
>> > The right side is to check whether the vcpus array is fully
>> > processed.
>> > When it is true and no error occurs (rc == 0), we
>> > update op->u.v.nr_vcpus, which is returned to libxc, and helps xc
>> > function figuring out how many un-processed vcpus should
>> > be taken care of in the next hypercall.
>> Just consider what the contents of op->u.v.nr_vcpus is after
>> this piece of code was executed, once with the full conditional,
>> and another time with the right side of the && omitted.
>>
> BTW, Chong, I'm not sure this has to do with what Jan is saying, but
> looking again at XEN_SYSCTL_pcitopoinfo, it looks to me you're missing
> copying nr_vcpus back up to the guest (which is actually what makes
> libxc knows whether all vcpus have been processed or now).

I think by "op->u.v.nr_vcpus = index", we already make the new nr_vcpus
seen by the guest (I've verified it).

In the case XEN_DOMCTL_scheduler_op of do_domctl(),
we make "copyback = 1" after calling sched_adjust(), which means all
fields in op (including
the new nr_vcpus) will be copied to u_domctl (at the end of
do_domctl()). This operation
ensures the new nr_vcpus is copied back up to the guest.

Please correct me if my understanding is wrong.

Chong

>
> Regards,
> Dario
> --
> <<This happens because I choose it to happen!>> (Raistlin Majere)
> -----------------------------------------------------------------
> Dario Faggioli, Ph.D, http://about.me/dario.faggioli
> Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
>



-- 
Chong Li
Department of Computer Science and Engineering
Washington University in St.louis

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