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: Monday, December 21, 2015 9:46 AM
> To: Wu, Feng <feng.wu@xxxxxxxxx>; pbonzini@xxxxxxxxxx;
> rkrcmar@xxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@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(-)
> >
> > diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> > index 84b96d3..c8c5f61 100644
> > --- a/arch/x86/kvm/irq_comm.c
> > +++ b/arch/x86/kvm/irq_comm.c
> > @@ -32,6 +32,7 @@
> >   #include "ioapic.h"
> >
> >   #include "lapic.h"
> > +#include "x86.h"
> >
> >   static int kvm_set_pic_irq(struct kvm_kernel_irq_routing_entry *e,
> >   			   struct kvm *kvm, int irq_source_id, int level,
> > @@ -53,8 +54,10 @@ static int kvm_set_ioapic_irq(struct
> kvm_kernel_irq_routing_entry *e,
> >   int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
> >   		struct kvm_lapic_irq *irq, unsigned long *dest_map)
> >   {
> > -	int i, r = -1;
> > +	int i, r = -1, idx = 0;
> >   	struct kvm_vcpu *vcpu, *lowest = NULL;
> > +	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
> > +	unsigned int dest_vcpus = 0;
> >
> >   	if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
> >   			kvm_lowest_prio_delivery(irq)) {
> > @@ -65,6 +68,8 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct
> kvm_lapic *src,
> >   	if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
> >   		return r;
> >
> > +	memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap));
> > +
> >   	kvm_for_each_vcpu(i, vcpu, kvm) {
> >   		if (!kvm_apic_present(vcpu))
> >   			continue;
> > @@ -78,13 +83,25 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct
> kvm_lapic *src,
> >   				r = 0;
> >   			r += kvm_apic_set_irq(vcpu, irq, dest_map);
> >   		} else if (kvm_lapic_enabled(vcpu)) {
> > -			if (!lowest)
> > -				lowest = vcpu;
> > -			else if (kvm_apic_compare_prio(vcpu, lowest) < 0)
> > -				lowest = vcpu;
> > +			if (!kvm_vector_hashing_enabled()) {
> > +				if (!lowest)
> > +					lowest = vcpu;
> > +				else if (kvm_apic_compare_prio(vcpu, lowest) <
> 0)
> > +					lowest = vcpu;
> > +			} else {
> > +				__set_bit(vcpu->vcpu_id, dest_vcpu_bitmap);
> > +				dest_vcpus++;
> > +			}
> >   		}
> >   	}
> >
> > +	if (dest_vcpus != 0) {
> > +		idx = kvm_vector_2_index(irq->vector, dest_vcpus,
> > +					 dest_vcpu_bitmap, KVM_MAX_VCPUS);
> > +
> > +		lowest = kvm_get_vcpu(kvm, idx - 1);
> > +	}
> > +
> >   	if (lowest)
> >   		r = kvm_apic_set_irq(lowest, irq, dest_map);
> >
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index ecd4ea1..e29001f 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -678,6 +678,22 @@ bool kvm_apic_match_dest(struct kvm_vcpu *vcpu,
> struct kvm_lapic *source,
> >   	}
> >   }
> >
> > +int kvm_vector_2_index(u32 vector, u32 dest_vcpus,
> > +		       const unsigned long *bitmap, u32 bitmap_size)
> > +{
> > +	u32 mod;
> > +	int i, idx = 0;
> > +
> > +	mod = vector % dest_vcpus;
> > +
> > +	for (i = 0; i <= mod; i++) {
> > +		idx = find_next_bit(bitmap, bitmap_size, idx) + 1;
> > +		BUG_ON(idx > bitmap_size);
> > +	}
> > +
> > +	return idx;
> > +}
> > +
> >   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!

Thanks,
Feng
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