kvm: Iterate over only vcpus that are preempted

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.

Reviewed-by: Chegu Vinod <chegu_vinod@hp.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 470f2bc..ff71541 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1768,6 +1768,8 @@ 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))