Re: [PATCH v2 0/9] qemu-kvm: Clean up and enhance MSI irqchip support

[Avi Kivity <avi@redhat.com>]

On 04/27/2011 12:00 PM, Jan Kiszka wrote:
> On 2011-04-27 09:27, Avi Kivity wrote:
> >  On 04/26/2011 04:19 PM, Jan Kiszka wrote:
> >>  I've still plans to consolidate MSI-X mask notifiers and KVM hooks, but
> >>  that can wait until we go upstream.
> >>
> >>  This version still makes classic MSI usable in irqchip mode, now not
> >>  only for PCI devices (AHCI, HDA) but also for the HPET (with msi=on).
> >>  Moreover, it contains an additional patch to refresh the MSI IRQ routes
> >>  after vmload.
> >>
> >
> >  Patches 1-8 applied, thanks.  I'm not sure about 9 (hpet kvm msi
> >  integration) - it seems very intrusive to do this to every
> >  msi-supporting device.  At least for pci we get all pci devices done in
> >  one shot.
>
> Right, it is a but intrusive, but I do not see any real alternative.
>
> >
> >  We could do this transparently in hw/apic.c.  When the message is sent
> >  for the first time we look it up, fail, and update the kvm routing
> >  entry.  Next time the lookup succeeds and we just use KVM_IRQ_LINE,
> >  until the message changes and we need to update the irq entry again.
>
> I thought about this, also for PCI devices that aren't assigned or
> vhost-driven, but we would quickly end up with unused and never freed
> IRQ routing entries. We still need to track the vector configurations.

We can simply drop all route entries that are used exclusively in qemu 
(i.e. not bound to an irqfd) and let the cache rebuild itself.

> What would help at least in the HPET case is a new DELIVER_MSI syscall
> that completely skips the IRQ routing thing.

It would only help users of 2.6.40 kernels.

> Actually, we only need
> routing for IRQs that shall be injected directly at kernel level. OTOH,
> this service would not be available on existing kernels, and we would
> not be able to simplify the PCI code that way (due to vhost
> requirements). So I dropped this idea as well and accepted that IRQ
> routing is the way to go.

I think that with the cache cleanup as outlined above it can work, no?

-- 
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