linux-kernel - Re: [PATCH] virtio_ring: remove unnecessary to

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Date:   Tue, 27 Sep 2022 16:30:02 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Bo Liu <liubo03@...pur.com>
Cc:     jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_ring: remove unnecessary to_vvq() call

On Mon, Sep 26, 2022 at 05:11:30AM -0400, Bo Liu wrote:
> It passes '_vq' to vring_free(), which still calls to_vvq()
> to get 'vq', let's directly pass 'vq'. It can avoid
> unnecessary call of to_vvq() in hot path.
> 
> Signed-off-by: Bo Liu <liubo03@...pur.com>

What is the point of this change?

__vring_new_virtqueue returns struct virtqueue *, so vring_free
matches that. No?

> ---
>  drivers/virtio/virtio_ring.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 8974c34b40fd..d6d77bf58802 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -221,7 +221,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index,
>  					       void (*callback)(struct virtqueue *),
>  					       const char *name);
>  static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num);
> -static void vring_free(struct virtqueue *_vq);
> +static void vring_free(struct vring_virtqueue *vq);
>  
>  /*
>   * Helpers.
> @@ -1140,7 +1140,7 @@ static int virtqueue_resize_split(struct virtqueue *_vq, u32 num)
>  	if (err)
>  		goto err_state_extra;
>  
> -	vring_free(&vq->vq);
> +	vring_free(vq);
>  
>  	virtqueue_vring_init_split(&vring_split, vq);
>  
> @@ -2059,7 +2059,7 @@ static int virtqueue_resize_packed(struct virtqueue *_vq, u32 num)
>  	if (err)
>  		goto err_state_extra;
>  
> -	vring_free(&vq->vq);
> +	vring_free(vq);
>  
>  	virtqueue_vring_init_packed(&vring_packed, !!vq->vq.callback);
>  
> @@ -2649,10 +2649,8 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
>  }
>  EXPORT_SYMBOL_GPL(vring_new_virtqueue);
>  
> -static void vring_free(struct virtqueue *_vq)
> +static void vring_free(struct vring_virtqueue *vq)
>  {
> -	struct vring_virtqueue *vq = to_vvq(_vq);
> -
>  	if (vq->we_own_ring) {
>  		if (vq->packed_ring) {
>  			vring_free_queue(vq->vq.vdev,
> @@ -2693,7 +2691,7 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>  	list_del(&_vq->list);
>  	spin_unlock(&vq->vq.vdev->vqs_list_lock);
>  
> -	vring_free(_vq);
> +	vring_free(vq);
>  
>  	kfree(vq);
>  }
> -- 
> 2.27.0