Re: Remaining passthrough/VT-d tasks list

["Yang, Sheng" <sheng.yang@intel.com>]

On Wednesday 24 September 2008 17:22:53 Avi Kivity wrote:
> Yang, Sheng wrote:
> >> We only have three pci interrupts at this point (though this could be
> >> easily extended); if you start the guest with a non-trivial number of
> >> devices, you will have shared guest interrupts.
> >>
> >> (of course, when I pointed this out during review, people said it could
> >> be done later, then forgot all about it)
> >
> > .....
> >
> > I think it's a performance issue, not break it? How about do it like Xen
> > side? Try best to avoid the share, extended the pci interrupts, improve
> > hash algorithm. Is there anything else we can do?
>
> Two separate issues:
>
> 1. only three guest pci interrupts
>
> That's a performance issue, not correctness.  can be fixed by using gsi
> 16-23 in APIC mode, and by adding another IOAPIC (so we can use gsi
> 16-47).  Anthony Xu posted some patches for this, not sure where this
> stands, but it was the right approach.
>
> 2. shared guest pci interrupts
>
> That's a correctness issue.  No matter how many interrupts we have, we
> may have sharing issues.  Of course with only three the issue is very
> pressing since we will get sharing with just a few devices.  Currently
> if two assigned devices share a guest interrupts, or if an emulated
> device shares an interrupt with an assigned device, things will break.
>
> They need to be fixed independently.

About the second issue, I don't understand how it would break... Would you 
please give more details on this? It's a QEmu bug or IOAPIC bug?

-- 
regards
Yang, Sheng