Re: [Xen-devel] xen-evtchn: Bind dyn evtchn:qemu-dm interrupt to next online CPU

[Anoob Soman <anoob.soman@xxxxxxxxxx>]

On 16/05/17 20:02, Boris Ostrovsky wrote:

Hi Boris,

Sorry for the delay, I was out traveling.

> >           rc = evtchn_bind_to_user(u, bind_interdomain.local_port);
> > -        if (rc == 0)
> > +        if (rc == 0) {
> >               rc = bind_interdomain.local_port;
> > +            selected_cpu = cpumask_next(selected_cpu, cpu_online_mask);
> > +            if (selected_cpu >= nr_cpu_ids)
> > +                selected_cpu = cpumask_first(cpu_online_mask);
> > +            xen_rebind_evtchn_to_cpu(rc, selected_cpu);
> Can you do proper assignment *instead of* binding to CPU0 as opposed to
> rebinding the event channel later? Otherwise you are making an extra
> hypercall.
If I understood the code correctly, EVTCHNOP_bind_interdomain doesn't 
support sending in VCPU number, so I think we would require two 
hypercalls one for binding interdomain eventchn 
(EVTCHNOP_bind_interdomain) and another for binding it to a VCPU 
(EVTCHNOP_bind_vcpu). We can create EVTCHNOP_bind_interdomain_V2 sub-op, 
which can take in VCPU id, if we want to avoid making multiple hypercalls.
> You also probably want to look at current IRQ affinity mask instead of
> cpu_online_mask.
Do we need to look at IRQ affinity mask, if we are going to bind 
eventchannel to smp_processor_id(). If we definitely need to use IRQ 
affinity then binding to smp_processor_id() might not be the correct 
approach.
-Anoob



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