[PATCH RFC 2/2] kvm: Iterate over only vcpus that are preempted

[Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>]

From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>

This helps in filtering out the eligible candidates further and 
thus potentially helps in quickly allowing preempted lockholders to run.
Note that if a vcpu was spinning during preemption we filter them
by checking whether they are preempted due to pause loop exit.

Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
---
 virt/kvm/kvm_main.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 83a804c..60114e1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1790,6 +1790,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
 				continue;
 			} else if (pass && i > last_boosted_vcpu)
 				break;
+			if (!ACCESS_ONCE(vcpu->preempted))
+				continue;
 			if (vcpu == me)
 				continue;
 			if (waitqueue_active(&vcpu->wq))