Messages in this thread | | | From | Wanpeng Li <> | Date | Tue, 11 Jun 2019 16:47:15 +0800 | Subject | Re: [PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall |
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On Mon, 10 Jun 2019 at 22:17, Radim Krčmář <rkrcmar@redhat.com> wrote: > > 2019-05-30 09:05+0800, Wanpeng Li: > > From: Wanpeng Li <wanpengli@tencent.com> > > > > The target vCPUs are in runnable state after vcpu_kick and suitable > > as a yield target. This patch implements the sched yield hypercall. > > > > 17% performance increasement of ebizzy benchmark can be observed in an > > over-subscribe environment. (w/ kvm-pv-tlb disabled, testing TLB flush > > call-function IPI-many since call-function is not easy to be trigged > > by userspace workload). > > > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > Cc: Radim Krčmář <rkrcmar@redhat.com> > > Cc: Liran Alon <liran.alon@oracle.com> > > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > > --- > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > @@ -7172,6 +7172,28 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu) > > kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu); > > } > > > > +static void kvm_sched_yield(struct kvm *kvm, unsigned long dest_id) > > +{ > > + struct kvm_vcpu *target = NULL; > > + struct kvm_apic_map *map = NULL; > > + > > + rcu_read_lock(); > > + map = rcu_dereference(kvm->arch.apic_map); > > + > > + if (unlikely(!map) || dest_id > map->max_apic_id) > > + goto out; > > + > > + if (map->phys_map[dest_id]->vcpu) { > > This should check for map->phys_map[dest_id].
Yeah, make a mistake here.
> > > + target = map->phys_map[dest_id]->vcpu; > > + rcu_read_unlock(); > > + kvm_vcpu_yield_to(target); > > + } > > + > > +out: > > + if (!target) > > + rcu_read_unlock(); > > Also, I find the following logic clearer > > { > struct kvm_vcpu *target = NULL; > struct kvm_apic_map *map; > > rcu_read_lock(); > map = rcu_dereference(kvm->arch.apic_map); > > if (likely(map) && dest_id <= map->max_apic_id && map->phys_map[dest_id]) > target = map->phys_map[dest_id]->vcpu; > > rcu_read_unlock(); > > if (target) > kvm_vcpu_yield_to(target); > }
More better, thanks.
Regards, Wanpeng Li
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