On 16/01/2009 06:18, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
>> I'd rather have all accesses mediated through pciback. I don't think PCI
>> config accesses should be on any data path anyway, and you've already taken
>> the hit of trapping to qemu in that case.
>
> There is one exception: The mask bit for MSI/MSI-X. Maybe we need add some
> mechanism for HVM domain to mask/unmask the virtual interrupt directly, like
> what DomU did for evtchn. But that will be tricky.
Yes, that did occur to me. We already have plenty of special emulation code
for MSI/MSI-x. I guess we may explicitly paravirtualise that aspect in a
different way which would allow ioemu to interact direct with Xen. Actually
if mask/unmask happens on every IRQ, we may need to push support for the PCI
MSI registers right down into Xen itself to get decent speed? Because going
to qemu with any great frequency is not very high performance.
 -- Keir
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