0002-Boost-vCPUs-based-on-IPI-sender-and-receiver-informa.patch

From 939c61e63dfe76e6dd609fa029c85ed055507344 Mon Sep 17 00:00:00 2001
From: Kenta Ishiguro <kentaishiguro@sslab.ics.keio.ac.jp>
Date: Wed, 14 Jul 2021 01:53:31 +0900
Subject: [PATCH 2/2] Boost vCPUs based on IPI-sender and receiver information

This commit monitors IPI communication between vCPUs and leverages the
relationship between vCPUs to select boost candidates.
---
 arch/x86/kvm/lapic.c     | 17 +++++++++++++++++
 arch/x86/kvm/x86.c       |  1 +
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      | 22 +++++++++++++++++-----
 4 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 7356a56e6282..c74b37654fd3 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1226,6 +1226,21 @@ void kvm_apic_set_eoi_accelerated(struct kvm_vcpu *vcpu, int vector)
 }
 EXPORT_SYMBOL_GPL(kvm_apic_set_eoi_accelerated);
 
+static void mark_ipi_receiver(struct kvm_lapic *apic, struct kvm_lapic_irq *irq)
+{
+	struct kvm_vcpu *dest_vcpu;
+	u64 prev_ipi_received;
+
+	dest_vcpu = kvm_get_vcpu_by_id(apic->vcpu->kvm, irq.dest_id);
+	if (!dest_vcpu)
+		return;
+
+	if (READ_ONCE(dest_vcpu->scheduled_out)) {
+		prev_ipi_received = READ_ONCE(dest_vcpu->ipi_received);
+		WRITE_ONCE(dest_vcpu->ipi_received, prev_ipi_received | (1ull << apic->vcpu->vcpu_id));
+	}
+}
+
 static void apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high)
 {
 	struct kvm_lapic_irq irq;
@@ -1244,6 +1259,8 @@ static void apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high)
 
 	trace_kvm_apic_ipi(icr_low, irq.dest_id);
 
+	mark_ipi_receiver(apic, &irq);
+
 	kvm_irq_delivery_to_apic(apic->vcpu->kvm, apic, &irq, NULL);
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cf95c36cb4f4..0d7e62efe2ca 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8357,6 +8357,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	trace_kvm_entry(vcpu->vcpu_id);
 	guest_enter_irqoff();
+	WRITE_ONCE(vcpu->ipi_received, 0);
 
 	fpregs_assert_state_consistent();
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index bcb9b2ac0791..ed9c0a3f168a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -317,6 +317,8 @@ struct kvm_vcpu {
 #endif
 	bool preempted;
 	bool ready;
+	bool scheduled_out;
+	u64 ipi_received;
 	struct kvm_vcpu_arch arch;
 	struct dentry *debugfs_dentry;
 };
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 70f03ce0e5c1..a9bfdf69cc7e 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -353,6 +353,8 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
 	kvm_vcpu_set_dy_eligible(vcpu, false);
 	vcpu->preempted = false;
 	vcpu->ready = false;
+	vcpu->scheduled_out = false;
+	vcpu->ipi_received = 0;
 	preempt_notifier_init(&vcpu->preempt_notifier, &kvm_preempt_ops);
 }
 
@@ -2655,6 +2657,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
 	struct kvm_vcpu *vcpu;
 	int last_boosted_vcpu = me->kvm->last_boosted_vcpu;
 	int yielded = 0;
+	u64 ipi_received;
 	int try = 3;
 	int pass;
 	int i;
@@ -2674,15 +2677,21 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
 				continue;
 			} else if (pass && i > last_boosted_vcpu)
 				break;
-			if (!READ_ONCE(vcpu->ready))
-				continue;
+			if (!READ_ONCE(vcpu->preempted)) {
+				ipi_received = READ_ONCE(vcpu->ipi_received);
+				if (!(READ_ONCE(vcpu->ready) && !!(ipi_received & (1ull << me->vcpu_id)))) {
+					WRITE_ONCE(vcpu->ipi_received, ipi_received | (1ull << me->vcpu_id));
+					continue;
+				}
+			}
 			if (vcpu == me)
 				continue;
 			if (swait_active(&vcpu->wq) && !vcpu_dy_runnable(vcpu))
 				continue;
-			if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
-				!kvm_arch_vcpu_in_kernel(vcpu))
-				continue;
+			if (yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu)) {
+				if (!(READ_ONCE(vcpu->ipi_received) & (1 << me->vcpu_id)))
+					continue;
+			}
 			if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
 				continue;
 
@@ -4388,6 +4397,8 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
 
 	WRITE_ONCE(vcpu->preempted, false);
 	WRITE_ONCE(vcpu->ready, false);
+	WRITE_ONCE(vcpu->scheduled_out, false);
+	WRITE_ONCE(vcpu->ipi_received, 0);
 
 	__this_cpu_write(kvm_running_vcpu, vcpu);
 	kvm_arch_sched_in(vcpu, cpu);
@@ -4403,6 +4414,7 @@ static void kvm_sched_out(struct preempt_notifier *pn,
 		WRITE_ONCE(vcpu->preempted, true);
 		WRITE_ONCE(vcpu->ready, true);
 	}
+	WRITE_ONCE(vcpu->scheduled_out, true);
 	kvm_arch_vcpu_put(vcpu);
 	__this_cpu_write(kvm_running_vcpu, NULL);
 }
-- 
2.20.1