[PATCH v2 1/2] KVM: Boosting vCPUs that are delivering interrupts

[Wanpeng Li]

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

Inspired by commit 9cac38dd5d (KVM/s390: Set preempted flag during vcpu wakeup 
and interrupt delivery), except the lock holder, we want to also boost vCPUs 
that are delivering interrupts. Actually most smp_call_function_many calls are 
synchronous ipi calls, the ipi target vCPUs are also good yield candidates. 
This patch introduces vcpu->ready to boost vCPUs during wakeup and interrupt 
delivery time.

Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM:
ebizzy -M

            vanilla     boosting    improved
1VM          21443       23520         9%                      
2VM           2800        8000       180%
3VM           1800        3100        72%

Testing on my Haswell desktop 8 HT, with 8 vCPUs VM 8GB RAM, two VMs, 
one running ebizzy -M, the other running 'stress --cpu 2':

w/ boosting + w/o pv sched yield(vanilla)   

            vanilla     boosting   improved 
              1570         4000      155%

w/ boosting + w/ pv sched yield(vanilla)

            vanilla     boosting   improved 
              1844         5157      179%   

w/o boosting, perf top in VM:

 72.33%  [kernel]       [k] smp_call_function_many
  4.22%  [kernel]       [k] call_function_i
  3.71%  [kernel]       [k] async_page_fault

w/ boosting, perf top in VM:

 38.43%  [kernel]       [k] smp_call_function_many
  6.31%  [kernel]       [k] async_page_fault
  6.13%  libc-2.23.so   [.] __memcpy_avx_unaligned
  4.88%  [kernel]       [k] call_function_interrupt

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
 arch/s390/kvm/interrupt.c |  2 +-
 include/linux/kvm_host.h  |  1 +
 virt/kvm/kvm_main.c       | 12 +++++++++---
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 9dde4d7..26f8bf4 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1240,7 +1240,7 @@ void kvm_s390_vcpu_wakeup(struct kvm_vcpu *vcpu)
 		 * The vcpu gave up the cpu voluntarily, mark it as a good
 		 * yield-candidate.
 		 */
-		vcpu->preempted = true;
+		vcpu->ready = true;
 		swake_up_one(&vcpu->wq);
 		vcpu->stat.halt_wakeup++;
 	}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c5da875..5c5b586 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -318,6 +318,7 @@ struct kvm_vcpu {
 	} spin_loop;
 #endif
 	bool preempted;
+	bool ready;
 	struct kvm_vcpu_arch arch;
 	struct dentry *debugfs_dentry;
 };
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b4ab59d..8412900 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2404,8 +2404,10 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
 	int me;
 	int cpu = vcpu->cpu;
 
-	if (kvm_vcpu_wake_up(vcpu))
+	if (kvm_vcpu_wake_up(vcpu)) {
+		vcpu->ready = true;
 		return;
+	}
 
 	me = get_cpu();
 	if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
@@ -2500,7 +2502,7 @@ 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->preempted))
+			if (!READ_ONCE(vcpu->ready))
 				continue;
 			if (vcpu == me)
 				continue;
@@ -4205,6 +4207,8 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
 
 	if (vcpu->preempted)
 		vcpu->preempted = false;
+	if (vcpu->ready)
+		vcpu->ready = false;
 
 	kvm_arch_sched_in(vcpu, cpu);
 
@@ -4216,8 +4220,10 @@ static void kvm_sched_out(struct preempt_notifier *pn,
 {
 	struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
 
-	if (current->state == TASK_RUNNING)
+	if (current->state == TASK_RUNNING) {
 		vcpu->preempted = true;
+		vcpu->ready = true;
+	}
 	kvm_arch_vcpu_put(vcpu);
 }
 
-- 
2.7.4