RE: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

[Wu, Feng]

> -----Original Message-----
> From: Yang Zhang [mailto:yang.zhang.wz@xxxxxxxxx]
> Sent: Tuesday, December 22, 2015 2:49 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>; pbonzini@xxxxxxxxxx;
> rkrcmar@xxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Jiang Liu
> (jiang.liu@xxxxxxxxxxxxxxx) <jiang.liu@xxxxxxxxxxxxxxx>
> Subject: Re: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-
> priority interrupts
> 
> >>>>
> >>>> On 2015/12/16 9:37, Feng Wu wrote:
> >>>>> Use vector-hashing to deliver lowest-priority interrupts, As an
> >>>>> example, modern Intel CPUs in server platform use this method to
> >>>>> handle lowest-priority interrupts.
> >>>>>
> >>>>> Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> >>>>> ---
> >>>>>     arch/x86/kvm/irq_comm.c | 27 ++++++++++++++++++-----
> >>>>>     arch/x86/kvm/lapic.c    | 57
> >>>> ++++++++++++++++++++++++++++++++++++++++---------
> >>>>>     arch/x86/kvm/lapic.h    |  2 ++
> >>>>>     arch/x86/kvm/x86.c      |  9 ++++++++
> >>>>>     arch/x86/kvm/x86.h      |  1 +
> >>>>>     5 files changed, 81 insertions(+), 15 deletions(-)
> >>>>>
> >>>>>     bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic
> >> *src,
> >>>>>     		struct kvm_lapic_irq *irq, int *r, unsigned long
> *dest_map)
> >>>>>     {
> >>>>> @@ -731,17 +747,38 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm
> >>>> *kvm, struct kvm_lapic *src,
> >>>>>     		dst = map->logical_map[cid];
> >>>>>
> >>>>>     		if (kvm_lowest_prio_delivery(irq)) {
> >>>>> -			int l = -1;
> >>>>> -			for_each_set_bit(i, &bitmap, 16) {
> >>>>> -				if (!dst[i])
> >>>>> -					continue;
> >>>>> -				if (l < 0)
> >>>>> -					l = i;
> >>>>> -				else if (kvm_apic_compare_prio(dst[i]->vcpu,
> >>>> dst[l]->vcpu) < 0)
> >>>>> -					l = i;
> >>>>> +			if (!kvm_vector_hashing_enabled()) {
> >>>>> +				int l = -1;
> >>>>> +				for_each_set_bit(i, &bitmap, 16) {
> >>>>> +					if (!dst[i])
> >>>>> +						continue;
> >>>>> +					if (l < 0)
> >>>>> +						l = i;
> >>>>> +					else if (kvm_apic_compare_prio(dst[i]-
> >>>>> vcpu, dst[l]->vcpu) < 0)
> >>>>> +						l = i;
> >>>>> +				}
> >>>>> +				bitmap = (l >= 0) ? 1 << l : 0;
> >>>>> +			} else {
> >>>>> +				int idx = 0;
> >>>>> +				unsigned int dest_vcpus = 0;
> >>>>> +
> >>>>> +				for_each_set_bit(i, &bitmap, 16) {
> >>>>> +					if (!dst[i]
> >>>> && !kvm_lapic_enabled(dst[i]->vcpu)) {
> >>>>
> >>>> It should be or(||) not and (&&).
> >>>
> >>> Oh, you are right! My negligence! Thanks for pointing this out, Yang!
> >>
> >> btw, i think the kvm_lapic_enabled check is wrong here? Why need it here?
> >
> > If the lapic is not enabled, I think we cannot recognize it as a candidate, can
> we?
> > Maybe Radim can confirm this, Radim, what is your option?
> 
> Lapic can be disable by hw or sw. Here we only need to check the hw is
> enough which is already covered while injecting the interrupt into
> guest. I remember we(Glab, Macelo and me) have discussed it several ago,
> but i cannot find the mail thread.

But if the lapic is disabled by software, we cannot still inject interrupts to
it, can we?

Thanks,
Feng
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