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

[Yang Zhang <yang.zhang.wz@gmail.com>]

On 2015/12/21 9:50, Wu, Feng wrote:
>
>
>> -----Original Message-----
>> From: Yang Zhang [mailto:yang.zhang.wz@gmail.com]
>> Sent: Monday, December 21, 2015 9:46 AM
>> To: Wu, Feng <feng.wu@intel.com>; pbonzini@redhat.com;
>> rkrcmar@redhat.com
>> Cc: kvm@vger.kernel.org; linux-kernel@vger.kernel.org
>> 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@intel.com>
>>> ---
>>>    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!

btw, i think the kvm_lapic_enabled check is wrong here? Why need it here?

>
> Thanks,
> Feng
>


-- 
best regards
yang