| Message ID | 20240506101751.3145407-3-foxywang@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: irqchip: synchronize srcu only if needed | expand |
On Mon, May 06, 2024, Yi Wang wrote: > From: Yi Wang <foxywang@tencent.com> > > 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@tencent.com> > --- > 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.
On Tue, Jun 11, 2024 at 8:25 AM Sean Christopherson <seanjc@google.com> wrote: > > On Mon, May 06, 2024, Yi Wang wrote: > > From: Yi Wang <foxywang@tencent.com> > > > > 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@tencent.com> > > --- > > 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
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[] = {}; -int kvm_setup_empty_irq_routing(struct kvm *kvm) -{ - return kvm_set_irq_routing(kvm, empty_routing, 0, 0); -} - void kvm_arch_post_irq_routing_update(struct kvm *kvm) { if (!irqchip_split(kvm)) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 91478b769af0..01270182757b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6527,9 +6527,6 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, goto split_irqchip_unlock; if (kvm->created_vcpus) goto split_irqchip_unlock; - r = kvm_setup_empty_irq_routing(kvm); - if (r) - goto split_irqchip_unlock; /* Pairs with irqchip_in_kernel. */ smp_wmb(); kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;