KVM: use heuristic for fast VCPU lookup by id

Usually, VCPU ids match the array index. So let's try a fast
lookup first before falling back to the slow iteration.

Suggested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 29119193a19f..a754fc08e194 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -472,6 +472,11 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
         struct kvm_vcpu *vcpu;
         int i;
 
+        if (id < 0 || id >= KVM_MAX_VCPUS)
+                return NULL;
+        vcpu = kvm_get_vcpu(kvm, id);
+        if (vcpu && vcpu->vcpu_id == id)
+                return vcpu;
         kvm_for_each_vcpu(i, vcpu, kvm)
                 if (vcpu->vcpu_id == id)
                         return vcpu;