Re: [PATCH] KVM: LAPIC: micro-optimize fixed mode ipi delivery

[Wanpeng Li]

ping,
On Fri, 20 Sep 2019 at 18:07, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> After disabling mwait/halt/pause vmexits, RESCHEDULE_VECTOR and
> CALL_FUNCTION_SINGLE_VECTOR etc IPI is one of the main remaining
> cause of vmexits observed in product environment which can't be
> optimized by PV IPIs. This patch is the follow-up on commit
> 0e6d242eccdb (KVM: LAPIC: Micro optimize IPI latency), to optimize
> redundancy logic before fixed mode ipi is delivered in the fast
> path.
>
> - broadcast handling needs to go slow path, so the delivery mode repair
>   can be delayed to before slow path.
> - self-IPI will not be intervened by hypervisor any more after APICv is
>   introduced and the boxes support APICv are popular now. In addition,
>   kvm_apic_map_get_dest_lapic() can handle the self-IPI, so there is no
>   need a shortcut for the non-APICv case.
>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
>  arch/x86/kvm/irq_comm.c | 6 +++---
>  arch/x86/kvm/lapic.c    | 5 -----
>  2 files changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index 8ecd48d..aa88156 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -52,15 +52,15 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
>         unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
>         unsigned int dest_vcpus = 0;
>
> +       if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
> +               return r;
> +
>         if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
>                         kvm_lowest_prio_delivery(irq)) {
>                 printk(KERN_INFO "kvm: apic: phys broadcast and lowest prio\n");
>                 irq->delivery_mode = APIC_DM_FIXED;
>         }
>
> -       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) {
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 323bdca..d77fe29 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -955,11 +955,6 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
>
>         *r = -1;
>
> -       if (irq->shorthand == APIC_DEST_SELF) {
> -               *r = kvm_apic_set_irq(src->vcpu, irq, dest_map);
> -               return true;
> -       }
> -
>         rcu_read_lock();
>         map = rcu_dereference(kvm->arch.apic_map);
>
> --
> 2.7.4
>