On 24/07/2019 10:04, Xiangyou Xie wrote:
> During the halt polling process, vgic_cpu->ap_list_lock is frequently
> obtained andreleased, (kvm_vcpu_check_block->kvm_arch_vcpu_runnable->
> kvm_vgic_vcpu_pending_irq).This action affects the performance of virq
> interrupt injection, because vgic_queue_irq_unlock also attempts to get
> vgic_cpu->ap_list_lock and add irq to vgic_cpu ap_list.
Numbers. Give me numbers. Please.
>
> The irq pending state and the minimum priority introduced by the patch,
> kvm_vgic_vcpu_pending_irq do not need to traverse vgic_cpu ap_list, only
> the check pending state and priority.
>
> Signed-off-by: Xiangyou Xie <xiexiangyou@xxxxxxxxxx>
> ---
> include/kvm/arm_vgic.h | 5 +++++
> virt/kvm/arm/vgic/vgic.c | 40 ++++++++++++++++++++++------------------
> 2 files changed, 27 insertions(+), 18 deletions(-)
>
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index ce372a0..636db29 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -337,6 +337,11 @@ struct vgic_cpu {
>
> /* Cache guest interrupt ID bits */
> u32 num_id_bits;
> +
> + /* Minimum of priority in all irqs */
> + u8 lowest_priority;
In all IRQs? That are in every possible state?
> + /* Irq pending flag */
> + bool pending;
What does pending mean here? Strictly pending? or covering the other
states of an interrupt (Active, Active+Pending)?
> };
>
> extern struct static_key_false vgic_v2_cpuif_trap;
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index deb8471..767dfe0 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -398,6 +398,12 @@ bool vgic_queue_irq_unlock(struct kvm *kvm, struct vgic_irq *irq,
> * now in the ap_list.
> */
> vgic_get_irq_kref(irq);
> +
> + if (!irq->active) {
Why not active? What if the interrupt is Active+Pending? What is the
rational for this? This applies to the whole of this patch.
> + vcpu->arch.vgic_cpu.pending = true;
> + if (vcpu->arch.vgic_cpu.lowest_priority > irq->priority)
> + vcpu->arch.vgic_cpu.lowest_priority = irq->priority;
> + }
> list_add_tail(&irq->ap_list, &vcpu->arch.vgic_cpu.ap_list_head);
> irq->vcpu = vcpu;
>
> @@ -618,6 +624,9 @@ static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
> retry:
> raw_spin_lock(&vgic_cpu->ap_list_lock);
>
> + vgic_cpu->lowest_priority = U8_MAX;
> + vgic_cpu->pending = false;
> +
> list_for_each_entry_safe(irq, tmp, &vgic_cpu->ap_list_head, ap_list) {
> struct kvm_vcpu *target_vcpu, *vcpuA, *vcpuB;
> bool target_vcpu_needs_kick = false;
> @@ -649,6 +658,11 @@ static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
> }
>
> if (target_vcpu == vcpu) {
> + if (!irq->active) {
> + vgic_cpu->pending = true;
> + if (vgic_cpu->lowest_priority > irq->priority)
> + vgic_cpu->lowest_priority = irq->priority;
> + }
> /* We're on the right CPU */
> raw_spin_unlock(&irq->irq_lock);
> continue;
> @@ -690,6 +704,11 @@ static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
>
> list_del(&irq->ap_list);
> irq->vcpu = target_vcpu;
> + if (!irq->active) {
> + new_cpu->pending = true;
> + if (new_cpu->lowest_priority > irq->priority)
> + new_cpu->lowest_priority = irq->priority;
> + }
> list_add_tail(&irq->ap_list, &new_cpu->ap_list_head);
> target_vcpu_needs_kick = true;
> }
> @@ -930,9 +949,6 @@ void kvm_vgic_put(struct kvm_vcpu *vcpu)
> int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu)
> {
> struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> - struct vgic_irq *irq;
> - bool pending = false;
> - unsigned long flags;
> struct vgic_vmcr vmcr;
>
> if (!vcpu->kvm->arch.vgic.enabled)
> @@ -943,22 +959,10 @@ int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu)
>
> vgic_get_vmcr(vcpu, &vmcr);
>
> - raw_spin_lock_irqsave(&vgic_cpu->ap_list_lock, flags);
> -
> - list_for_each_entry(irq, &vgic_cpu->ap_list_head, ap_list) {
> - raw_spin_lock(&irq->irq_lock);
> - pending = irq_is_pending(irq) && irq->enabled &&
> - !irq->active &&
> - irq->priority < vmcr.pmr;
> - raw_spin_unlock(&irq->irq_lock);
> -
> - if (pending)
> - break;
> - }
> -
> - raw_spin_unlock_irqrestore(&vgic_cpu->ap_list_lock, flags);
> + if (vgic_cpu->pending && vgic_cpu->lowest_priority < vmcr.pmr)
> + return true;
And here we go. You've dropped the lock, and yet are evaluating two
unrelated fields that could be changed by a parallel injection or the
vcpu entering/exiting the guest.
I'm sure you get better performance. I'm also pretty sure this is
completely unsafe.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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