> On 28 May 2019, at 3:53, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> The target vCPUs are in runnable state after vcpu_kick and suitable
> as a yield target. This patch implements the sched yield hypercall.
>
> 17% performace increase 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@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e7e57de..2ceef51 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7172,6 +7172,26 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
> kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
> }
>
> +void kvm_sched_yield(struct kvm *kvm, u64 dest_id)
> +{
> + struct kvm_vcpu *target;
> + struct kvm_apic_map *map;
> +
> + rcu_read_lock();
> + map = rcu_dereference(kvm->arch.apic_map);
> +
> + if (unlikely(!map))
> + goto out;
> +
We should have a bounds-check here on “dest_id”.
-Liran
> + if (map->phys_map[dest_id]->vcpu) {
> + target = map->phys_map[dest_id]->vcpu;
> + kvm_vcpu_yield_to(target);
> + }
> +
> +out:
> + rcu_read_unlock();
> +}
> +
> int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> {
> unsigned long nr, a0, a1, a2, a3, ret;
> @@ -7218,6 +7238,10 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> case KVM_HC_SEND_IPI:
> ret = kvm_pv_send_ipi(vcpu->kvm, a0, a1, a2, a3, op_64_bit);
> break;
> + case KVM_HC_SCHED_YIELD:
> + kvm_sched_yield(vcpu->kvm, a0);
> + ret = 0;
> + break;
> default:
> ret = -KVM_ENOSYS;
> break;
> --
> 2.7.4
>
