RE: [Xen-devel] RE: Rather slow time of Pin in Windows with GPL PVdriver

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

Yeah, you're right. We have a patch in XenServer to just use the lowest 
numbered vCPU but in unstable it still pointlessly round robins. Thus, if you 
bind DPCs and don't set their importance up you will end up with them not being 
immediately scheduled quite a lot of the time.

  Paul

> -----Original Message-----
> From: James Harper [mailto:james.harper@xxxxxxxxxxxxxxxx]
> Sent: 10 March 2011 09:30
> To: Paul Durrant; MaoXiaoyun
> Cc: xen devel
> Subject: RE: [Xen-devel] RE: Rather slow time of Pin in Windows with
> GPL PVdriver
> 
> >
> > You have to be careful here. Xen will only ever deliver the evtchn
> interrupt
> > to VCPU0. I can't immediately see anything preventing an HVM
> domain
> trying to
> > bind and evtchn to another VCPU but you can see from the code in
> > hvm_assert_evtchn_irq() that the guest will only be kicked for
> events
> bound to
> > VCPU0 (is_hvm_pv_evtchn_vcpu() will only be true for Linux PVonHVM
> domains).
> > Thus if you bind your DPC to a CPU other than zero and don't set
> it to
> > HighImportance then it will not be immediately scheduled since
> default
> DPC
> > importance is MediumImportance.
> >
> 
> Are you sure? That's not what I remember seeing. You always have to
> query shared_info_area->vcpu_info[0] not shared_info_area-
> >vcpu_info[vcpu], but the actual VCPU the interrupt is scheduled
> onto can be any.
> 
> James

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