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

[Yang Zhang]

On 2015/12/22 14:59, Wu, Feng wrote:
> > -----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?

Yes, We cannot inject the normal interrupt. But this already covered by 
current logic and add a check here seems meaningless. Conversely, it may 
do bad thing..

--
best regards
yang
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