lkml.org 
[lkml]   [2019]   [Nov]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 2/2] KVM: LAPIC: micro-optimize fixed mode ipi delivery
From
Date
On 09/11/19 08:05, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> 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.

I agree with this part, but is the cost of the irq->shorthand check
really measurable?

Paolo

> - 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@tencent.com>
> ---
> 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 b29d00b..ea936fa 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -951,11 +951,6 @@ 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);
>
>

\
 
 \ /
  Last update: 2019-11-11 22:59    [W:0.122 / U:3.712 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site