On 20/03/17 10:58, Christoffer Dall wrote:
> There is no need to call any functions to fold LRs when we don't use any
> LRs and we don't need to mess with overflow flags, take spinlocks, or
> prune the AP list if the AP list is empty.
>
> Note: list_empty is a single atomic read (uses READ_ONCE) and can
> therefore check if a list is empty or not without the need to take the
> spinlock protecting the list.
>
> Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx>
> ---
> virt/kvm/arm/vgic/vgic.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 093873e..8ecb009 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -639,15 +639,18 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
> {
> struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>
> - if (unlikely(!vgic_initialized(vcpu->kvm)))
Could this be folded with the previous patch? It is the same optimisation.
> + /* An empty ap_list_head implies used_lrs == 0 */
> + if (list_empty(&vcpu->arch.vgic_cpu.ap_list_head))
> return;
>
> vgic_clear_uie(vcpu);
> - vgic_fold_lr_state(vcpu);
> - vgic_prune_ap_list(vcpu);
>
> - /* Make sure we can fast-path in flush_hwstate */
> - vgic_cpu->used_lrs = 0;
> + if (vgic_cpu->used_lrs) {
> + vgic_fold_lr_state(vcpu);
> + vgic_cpu->used_lrs = 0;
This zeroing could also be moved to vgic_fold_lr_state(), though I don't
feel strongly about it.
> + }
> +
> + vgic_prune_ap_list(vcpu);
> }
>
> /* Flush our emulation state into the GIC hardware before entering the guest. */
>
Otherwise looks good to me.
M.
--
Jazz is not dead. It just smells funny...
