[dpdk-dev] [PATCH v5 2/6] vhost: rewrite enqueue

[Maxime Coquelin]

On 09/09/2016 05:39 AM, Zhihong Wang wrote:
>
> +static inline void __attribute__((always_inline))
> +notify_guest(struct virtio_net *dev, struct vhost_virtqueue *vq)
> +{
>       rte_smp_wmb();
> -
> -     *(volatile uint16_t *)&vq->used->idx += count;
> -     vq->last_used_idx += count;
> -     vhost_log_used_vring(dev, vq,
> -             offsetof(struct vring_used, idx),
> -             sizeof(vq->used->idx));
> -
> -     /* flush used->idx update before we read avail->flags. */
Please don't remove comments if not justified.
Here the comment is important, as it explains why the barrier is needed.
> +     *(volatile uint16_t *)&vq->used->idx = vq->last_used_idx;
> +     vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
> +                     sizeof(vq->used->idx));
>       rte_mb();
> -
> -     /* Kick the guest if necessary. */
>       if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
>                       && (vq->callfd >= 0))
>               eventfd_write(vq->callfd, (eventfd_t)1);
> -     return count;
>  }