Re: [PATCH 09/10] KVM: Enable MSI for device assignment

[Avi Kivity <avi@redhat.com>]

Sheng Yang wrote:
> One question here: did the architectures other than X86 and IA64 need
> dispatch MSI support?  

s390 doesn't.  ppc may, one day in the future.  Not now I think.

> If so, I am afraid reuse assigned_device_msi_dispatch
> (or similar solution) won't be elegant (though I already lean toward a arch
> specific dispatch function).
>
> I am not familiar with virtio-pci and how it works, it would be good if
> it can be illustrated a little more. 

For this context, it's just a pci device.  qemu calls KVM_IRQ_LINE to 
inject an irq, and the pci layer in the guest delivers the irq to the 
virtio-pci driver.

In fact, it's not just for pci.  We could msi-enable e1000 and get 
improved performance there as well.

> But I guess what you means is only set
> gsi can result in kvm_set_irq() deliver the MSI correctly. I think this can
> be done. Associating gsi with guest_msi_addr and guest_msi_data in a linked
> list, for gsi >= IOAPIC_PINS,
Let's say, (gsi >> 24) == 1.  That gives us 16M potential MSIs.

>  kvm_set_irq() checked the list and deliver the
> interrupt. Of course, some lock should be taken to maintain the list, maybe
> kvm->lock in first step as we used for kvm_set_irq (kvm->lock become more
> and more bigger...).
>   

I think kvm_set_irq() already takes kvm->lock.

-- 
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