Re: [PATCH v2 6/9] virtio_net: transmit the multi-buffer xdp

[Jason Wang <jasowang@xxxxxxxxxx>]

在 2022/12/27 16:26, Heng Qi 写道:
> 在 2022/12/27 下午3:12, Jason Wang 写道:
> > 在 2022/12/20 22:14, Heng Qi 写道:
> > > This serves as the basis for XDP_TX and XDP_REDIRECT
> > > to send a multi-buffer xdp_frame.
> > >
> > > Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> > > Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/net/virtio_net.c | 27 ++++++++++++++++++++++-----
> > >   1 file changed, 22 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 40bc58fa57f5..9f31bfa7f9a6 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -563,22 +563,39 @@ static int __virtnet_xdp_xmit_one(struct 
> > > virtnet_info *vi,
> > >                      struct xdp_frame *xdpf)
> > >   {
> > >       struct virtio_net_hdr_mrg_rxbuf *hdr;
> > > -    int err;
> > > +    struct skb_shared_info *shinfo;
> > > +    u8 nr_frags = 0;
> > > +    int err, i;
> > >         if (unlikely(xdpf->headroom < vi->hdr_len))
> > >           return -EOVERFLOW;
> > >   -    /* Make room for virtqueue hdr (also change xdpf->headroom?) */
> > > +    if (unlikely(xdp_frame_has_frags(xdpf))) {
> > > +        shinfo = xdp_get_shared_info_from_frame(xdpf);
> > > +        nr_frags = shinfo->nr_frags;
> > > +    }
> > > +
> > > +    /* Need to adjust this to calculate the correct postion
> > > +     * for shinfo of the xdpf.
> > > +     */
> > > +    xdpf->headroom -= vi->hdr_len;
> >
> >
> > Any reason we need to do this here? (Or if it is, is it only needed 
> > for multibuffer XDP?)
>
> Going back to its wrapping function virtnet_xdp_xmit(), we need to 
> free up the pending old buffers.
> If the "is_xdp_frame(ptr)" condition is met, then we need to calculate 
> the position of skb_shared_info
> in xdp_get_frame_len() and xdp_return_frame(), which will involve to 
> xdpf->data and xdpf->headroom.
> Therefore, we need to update the value of headroom synchronously here.


Let's tweak the comment above to something like this.

With that fixed,

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

Thanks


> Also, it's not necessary for single-buffer xdp, but we need to keep it 
> because it's harmless and as it should be.
>
> Thanks.
>
> > Other looks good.
> >
> > Thanks
> >
> >
> > >       xdpf->data -= vi->hdr_len;
> > >       /* Zero header and leave csum up to XDP layers */
> > >       hdr = xdpf->data;
> > >       memset(hdr, 0, vi->hdr_len);
> > >       xdpf->len   += vi->hdr_len;
> > >   -    sg_init_one(sq->sg, xdpf->data, xdpf->len);
> > > +    sg_init_table(sq->sg, nr_frags + 1);
> > > +    sg_set_buf(sq->sg, xdpf->data, xdpf->len);
> > > +    for (i = 0; i < nr_frags; i++) {
> > > +        skb_frag_t *frag = &shinfo->frags[i];
> > > +
> > > +        sg_set_page(&sq->sg[i + 1], skb_frag_page(frag),
> > > +                skb_frag_size(frag), skb_frag_off(frag));
> > > +    }
> > >   -    err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdpf),
> > > -                   GFP_ATOMIC);
> > > +    err = virtqueue_add_outbuf(sq->vq, sq->sg, nr_frags + 1,
> > > +                   xdp_to_ptr(xdpf), GFP_ATOMIC);
> > >       if (unlikely(err))
> > >           return -ENOSPC; /* Caller handle free/refcnt */