linux-kernel - Re: [RFC PATCH 2/4] drivers/net/virtio_net: Changed mergeable buffer length calculation.

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Date:   Mon, 1 Nov 2021 04:44:00 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Andrew Melnychenko <andrew@...nix.com>
Cc:     jasowang@...hat.com, davem@...emloft.net, kuba@...nel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, yuri.benditovich@...nix.com,
        yan@...nix.com
Subject: Re: [RFC PATCH 2/4] drivers/net/virtio_net: Changed mergeable buffer
 length calculation.

On Sun, Oct 31, 2021 at 06:59:57AM +0200, Andrew Melnychenko wrote:
> Now minimal virtual header length is may include the entire v1 header
> if the hash report were populated.
> 
> Signed-off-by: Andrew Melnychenko <andrew@...nix.com>

subject isn't really descriptive. changed it how?

And I couldn't really decypher what this log entry means either.

> ---
>  drivers/net/virtio_net.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index b72b21ac8ebd..abca2e93355d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -393,7 +393,9 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  	hdr_p = p;
>  
>  	hdr_len = vi->hdr_len;
> -	if (vi->mergeable_rx_bufs)
> +	if (vi->has_rss_hash_report)
> +		hdr_padded_len = sizeof(struct virtio_net_hdr_v1_hash);
> +	else if (vi->mergeable_rx_bufs)
>  		hdr_padded_len = sizeof(*hdr);
>  	else
>  		hdr_padded_len = sizeof(struct padded_vnet_hdr);
> @@ -1252,7 +1254,7 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
>  					  struct ewma_pkt_len *avg_pkt_len,
>  					  unsigned int room)
>  {
> -	const size_t hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> +	const size_t hdr_len = ((struct virtnet_info *)(rq->vq->vdev->priv))->hdr_len;
>  	unsigned int len;
>  
>  	if (room)

Is this pointer chasing the best we can do?

> @@ -2817,7 +2819,7 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
>   */
>  static unsigned int mergeable_min_buf_len(struct virtnet_info *vi, struct virtqueue *vq)
>  {
> -	const unsigned int hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> +	const unsigned int hdr_len = vi->hdr_len;
>  	unsigned int rq_size = virtqueue_get_vring_size(vq);
>  	unsigned int packet_len = vi->big_packets ? IP_MAX_MTU : vi->dev->max_mtu;
>  	unsigned int buf_len = hdr_len + ETH_HLEN + VLAN_HLEN + packet_len;
> -- 
> 2.33.1