Re: [Xen-devel][RFC]degradation on IPF due to hypercall set irq

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 22/11/06 3:33 am, "Xu, Anthony" <anthony.xu@xxxxxxxxx> wrote:

> After moving from sharing PIC to hypercall set irq.
> KB on UP VTI domain incurs > 10% degradation.
> 
> The root cause is hypercall is very expensive on IPF side
> due to huge processor context.
> 
> I revert to sharing PIC in lastest Cset of IPF side,
> Then We can get performance back.

We may well have similar degradation on x86 too. The cause is lots of
unnecessary calls to the set_level hypercall (when the level hasn't actually
changed). Qemu *definitely* needs to keep shadow wire state and only notify
Xen on transitions. If the rate of hypercalls is still too high (which I
think is unlikely) we can use batching multicalls.

> I prepare to use shared IOSAPIC to deliver interrupt from
> Qemu to VTI domain.
> In IPF side, PIC is not needed,
> In the same time, we can assign more interrupt pins(24) to qemu.

I moved x86 away from this on purpose, to obtain a clean abstraction. I
don't think it's a good idea for ia64 to step backwards here.

 -- Keir



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