Messages in this thread | | | Date | Fri, 9 Jan 2015 16:12:59 +0100 | From | Radim Krčmář <> | Subject | Re: [v3 13/26] KVM: Define a new interface kvm_find_dest_vcpu() for VT-d PI |
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2015-01-09 15:56+0100, Paolo Bonzini: > > > On 09/01/2015 15:54, Radim Krčmář wrote: > > There are two points relevant to this patch in new KVM's implementation, > > ("KVM: x86: amend APIC lowest priority arbitration", > > https://lkml.org/lkml/2015/1/9/362) > > > > 1) lowest priority depends on TPR > > 2) there is no need for balancing > > > > (1) has to be considered with PI as well. > > The chipset doesn't support it. :(
I meant that we need to recompute PI entries for lowest priority interrupts every time guest's TPR changes.
Luckily, Linux doesn't use TPR, but other OS might be a reason to drop lowest priority from PI optimizations. (Or make it more complicated.)
> > I kept (2) to avoid whining from people building on that behaviour, but > > lowest priority backed by PI could be transparent without it. > > > > Patch below removes the balancing, but I am not sure this is a price we > > allowed ourselves to pay ... what are your opinions? > > I wouldn't mind, but it requires a lot of benchmarking.
(I was afraid it would come to that.)
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