KVM: remember position in kvm->vcpus array

Fetching an index for any vcpu in kvm->vcpus array by traversing
the entire array everytime is costly.
This patch remembers the position of each vcpu in kvm->vcpus array
by storing it in vcpus_idx under kvm_vcpu structure.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a817e44..70b2296 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -266,7 +266,8 @@ struct kvm_vcpu {
        struct preempt_notifier preempt_notifier;
 #endif
        int cpu;
-       int vcpu_id;
+       int vcpu_id; /* id given by userspace at creation */
+       int vcpu_idx; /* index in kvm->vcpus array */
        int srcu_idx;
        int mode;
        u64 requests;
@@ -570,13 +571,7 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
 
 static inline int kvm_vcpu_get_idx(struct kvm_vcpu *vcpu)
 {
-       struct kvm_vcpu *tmp;
-       int idx;
-
-       kvm_for_each_vcpu(idx, tmp, vcpu->kvm)
-               if (tmp == vcpu)
-                       return idx;
-       BUG();
+       return vcpu->vcpu_idx;
 }
 
 #define kvm_for_each_memslot(memslot, slots)   \

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b8534c6..a158a93 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2685,7 +2685,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
                goto unlock_vcpu_destroy;
        }
 
-       BUG_ON(kvm->vcpus[atomic_read(&kvm->online_vcpus)]);
+       vcpu->vcpu_idx = atomic_read(&kvm->online_vcpus);
+       BUG_ON(kvm->vcpus[vcpu->vcpu_idx]);
 
        /* Now it's all set up, let userspace reach it */
        kvm_get_kvm(kvm);
@@ -2695,7 +2696,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
                goto unlock_vcpu_destroy;
        }
 
-       kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu;
+       kvm->vcpus[vcpu->vcpu_idx] = vcpu;
 
        /*
         * Pairs with smp_rmb() in kvm_get_vcpu.  Write kvm->vcpus