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

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

On 2015/12/16 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 (&&).

> +						__clear_bit(i, &bitmap);
> +						continue;
> +					}
> +				}
> +
> +				dest_vcpus = hweight16(bitmap);
> +
> +				if (dest_vcpus != 0) {
> +					idx = kvm_vector_2_index(irq->vector,
> +						dest_vcpus, &bitmap, 16);
> +
> +					bitmap = 0;
> +					__set_bit(idx-1, &bitmap);
> +				}
>   			}
> -
> -			bitmap = (l >= 0) ? 1 << l : 0;
>   		}
>   	}
>
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index fde8e35d..6890ef0 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -170,4 +170,6 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu);
>
>   bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
>   			struct kvm_vcpu **dest_vcpu);
> +int kvm_vector_2_index(u32 vector, u32 dest_vcpus,
> +		       const unsigned long *bitmap, u32 bitmap_size);
>   #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4a6eff1..fb47730 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -118,6 +118,9 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
>   unsigned int lapic_timer_advance_ns = 0;
>   module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR);
>
> +bool __read_mostly enable_vector_hashing = 1;
> +module_param(enable_vector_hashing, bool, S_IRUGO);
> +
>   static bool backwards_tsc_observed = false;
>
>   #define KVM_NR_SHARED_MSRS 16
> @@ -8165,6 +8168,12 @@ int kvm_arch_update_irqfd_routing(struct kvm *kvm, unsigned int host_irq,
>   	return kvm_x86_ops->update_pi_irte(kvm, host_irq, guest_irq, set);
>   }
>
> +bool kvm_vector_hashing_enabled(void)
> +{
> +	return enable_vector_hashing;
> +}
> +EXPORT_SYMBOL_GPL(kvm_vector_hashing_enabled);
> +
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index f2afa5f..04bd0f9 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -179,6 +179,7 @@ int kvm_mtrr_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data);
>   int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata);
>   bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
>   					  int page_num);
> +bool kvm_vector_hashing_enabled(void);
>
>   #define KVM_SUPPORTED_XCR0     (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
>   				| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
>


-- 
best regards
yang