Re: [Xen-devel] [query] gic_set_lr always uses maintenance Interrupt

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-11-07 at 22:14 +0530, Mj Embd wrote:
> On Thu, Nov 7, 2013 at 5:07 PM, Stefano Stabellini
> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > Please don't top post as it makes it harder to follow the conversation.
> >
> > On Thu, 7 Nov 2013, Mj Embd wrote:
> >> A few thoughts are circling around my mind, don't know how much
> >> interrupt latency would it have.
> >>
> >> Rather than the hypervisor entry when guest does EOI, a late / lazy
> >> checkin on LR's can be done
> >>  on next hypervisor entry by
> >> a) guest doing something and trapping to hypervisor
> >> b) schedular timer in hypervisor
> >>
> >> What do you think on this...
> >
> > It might work.
> > One key issue is how to identify that the guest EOIed a particular irq
> > and henceforth the corresponding LR can be reused.
> [mj] I believe that GICH_ELSR0/1 can be read anytime to get the status.
> 
> > I hope that the status bits in the LR register reflect this condition.
> > Maybe the status becomes 00 invalid after the guest does EOI? Otherwise
> [mj] The state in LR is marked invalid by Virtual CPU interface.

If you can make it work then we'd be interested in seeing the patches.

Ian.


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