RE: [Xen-devel] Move some of the PCI device manage/control into pciback?

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> 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.

We plan to do this for MSI-X firstly, since currently qemu does not present 
mask support for MSI interrupt.
And we do notice such issue for some OS (at least for those based on kernel 
2.6.18).

> 
> -- Keir
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