Re: QEMU PIC indirection patch for in-kernel APIC work

Nakajima, Jun
2007-04-04T16:20:57Z

Avi Kivity wrote:
> Anthony Liguori wrote:
>>
>>>
>>> This pushes towards in kernel apic too. Can't see how we avoid it.
>>>
>>
>> Does it really? IIUC, we would avoid TPR traps entirely and would
>> just need to synchronize the TPR whenever we go down to userspace.
>>
>
> It's a bit more complex than that, as userspace would need to tell the
> kernel the highest priority pending interrupt so that it can program
> the hardware to exit when an interrupt is ready. However I agree
> with you that in principle we could split the apic emulation between
> kvm and qemu, even with this featurette.

Most of H/W-virtualization capable processors out there don't support
that feature today. I think the decision (kvm or qemu) should be done
based on performance data. I'm not worried about maintenance issues; the
APIC code is not expected to change frequently. I'm a bit worried about
extra complexity caused by such split, though.

BTW, I see CPU utilization of qemu is almost always 99% in the top
command when I run kernel build in an x86-64 Linux guest.

Jun
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