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From:   Wanpeng Li <kernellwp@gmail.com>
To:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>
Subject: [PATCH v2 2/3] KVM: X86: Implement PV sched yield hypercall
Date:   Tue, 28 May 2019 08:53:14 +0800
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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% 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@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 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;
+
+	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