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

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Date:   Wed, 17 Nov 2021 08:00:00 +0200
From:   Andrew Melnichenko <andrew@...nix.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <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 <yuri.benditovich@...nix.com>,
        Yan Vugenfirer <yan@...nix.com>
Subject: Re: [RFC PATCH 2/4] drivers/net/virtio_net: Changed mergeable buffer
 length calculation.

On Mon, Nov 1, 2021 at 10:44 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> 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.
>

I'll change it in the next patch.
So, I've tried to ensure that the v1 header with the hash report will
be available if required in new patches.

> > ---
> >  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?

I'll change that.

>
> > @@ -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
>