On Wed, Nov 06, 2019 at 08:36:37AM -0500, Nitesh Narayan Lal wrote:
> From: Radim Krčmář <rkrcmar@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
> ---
> include/linux/kvm_host.h | 11 +++--------
> virt/kvm/kvm_main.c | 5 ++++-
> 2 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 719fc3e..31c4fde 100644
> --- 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 vcpus_idx; /* index in kvm->vcpus array */
I'd probably prefer vcpu_idx or vcpu_index, but it's not a strong
preference by any means.
> int srcu_idx;
> int mode;
> u64 requests;
> @@ -571,13 +572,7 @@ 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->vcpus_idx;
> }
>
> #define kvm_for_each_memslot(memslot, slots) \
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 67ef3f2..24ab711 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2673,7 +2673,10 @@ 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->vcpus_idx = atomic_read(&kvm->online_vcpus);
> +
Nit: I'd omit this newline since the assignment and BUG_ON() are directly
related.
> + BUG_ON(kvm->vcpus[vcpu->vcpus_idx]);
The assignment to kvm->vcpus a few lines below should be updated to use
the new index.
> +
>
> /* Now it's all set up, let userspace reach it */
> kvm_get_kvm(kvm);
> --
> 1.8.3.1
>
