On Tue, Jun 11, 2024 at 8:25 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Mon, May 06, 2024, Yi Wang wrote:
> > From: Yi Wang <foxywang@xxxxxxxxxxx>
> >
> > We found that it may cost more than 20 milliseconds very accidentally
> > to enable cap of KVM_CAP_SPLIT_IRQCHIP on a host which has many vms
> > already.
> >
> > The reason is that when vmm(qemu/CloudHypervisor) invokes
> > KVM_CAP_SPLIT_IRQCHIP kvm will call synchronize_srcu_expedited() and
> > might_sleep and kworker of srcu may cost some delay during this period.
> >
> > As we have set up empty irq routing when creating vm, so this is no
> > need now.
> >
> > Signed-off-by: Yi Wang <foxywang@xxxxxxxxxxx>
> > ---
> > arch/x86/kvm/irq.h | 1 -
> > arch/x86/kvm/irq_comm.c | 5 -----
> > arch/x86/kvm/x86.c | 3 ---
> > 3 files changed, 9 deletions(-)
> >
> > diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
> > index c2d7cfe82d00..76d46b2f41dd 100644
> > --- a/arch/x86/kvm/irq.h
> > +++ b/arch/x86/kvm/irq.h
> > @@ -106,7 +106,6 @@ void __kvm_migrate_timers(struct kvm_vcpu *vcpu);
> > int apic_has_pending_timer(struct kvm_vcpu *vcpu);
> >
> > int kvm_setup_default_irq_routing(struct kvm *kvm);
> > -int kvm_setup_empty_irq_routing(struct kvm *kvm);
> > int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
> > struct kvm_lapic_irq *irq,
> > struct dest_map *dest_map);
> > diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> > index 68f3f6c26046..6ee7ca39466e 100644
> > --- a/arch/x86/kvm/irq_comm.c
> > +++ b/arch/x86/kvm/irq_comm.c
> > @@ -397,11 +397,6 @@ int kvm_setup_default_irq_routing(struct kvm *kvm)
> >
> > static const struct kvm_irq_routing_entry empty_routing[] = {};
>
> empty_routing is unused after this patch and can+should be removed, e.g.
>
> arch/x86/kvm/irq_comm.c:398:43: error: ‘empty_routing’ defined but not used [-Werror=unused-const-variable=]
> 398 | static const struct kvm_irq_routing_entry empty_routing[] = {};
>
> I'll fix this up when applying, too.
Many thanks for your work, Sean.
---
Best wishes
Yi Wang
