Re: [RFC PATCH 00/18] KVM: x86: CPU isolation and direct interrupts handling by guests

Avi Kivity
2012-06-28T17:35:01Z

On 06/28/2012 08:26 PM, Jan Kiszka wrote:
>>
>> This is both impressive and scary. What is the target scenario here?
>> Partitioning? I don't see this working for generic consolidation.
>>
>
> From my POV, partitioning - including hard realtime partitions - would
> provide some use cases. But, as far as I saw, there are still major
> restrictions in this approach, e.g. that you can't return to userspace
> on the slave core. Or even execute the in-kernel device models on that core.
>
> I think we need something based on the no-hz work on the long run, ie.
> the ability to run a single VCPU thread of the userland hypervisor on a
> single core with zero rescheduling and unrelated interruptions - as far
> as the guest load scenario allows this (we have some here).

What we can do perhaps is switch from direct mode to indirect mode on
exit. Instead of running with interrupts disabled, enable interrupts
and make sure they are forwarded to the guest on the next entry.

> Well, and we need proper hardware support for direct IRQ injection on x86...

Hardware support always helps, but it always seems to come after the
software support is in place and needs to be supported forever.

--
error compiling committee.c: too many arguments to function