On Mon, Apr 17, 2023 at 07:03:52AM +0000, Alvaro Karsz
wrote:> > > > Actually, I think that all you need to do is disable
NETIF_F_SG,
> > > > and things will work, no?
> > >
> > > I think that this is not so simple, if I understand correctly, by
disabling NETIF_F_SG we will never receive a chained skbs to transmit, but we
still have more functionality to address, for example:
> > > * The TX timeouts.
> >
> > I don't get it. With a linear skb we can transmit it as long as
there's
> > space for 2 entries in the vq: header and data. What's the source
of the
> > timeouts?
> >
>
> I'm not saying that this is not possible, I meant that we need more
changes to virtio-net.
> The source of the timeouts is from the current implementation of
virtnet_poll_tx.
>
> if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> netif_tx_wake_queue(txq);
Oh right. So this should check NETIF_F_SG then.
BTW both ring size and s/g can be tweaked by ethtool, also
needs handling.
>
> > > * Guest GSO/big MTU (without VIRTIO_NET_F_MRG_RXBUF?), we
can't chain page size buffers anymore.
> >
> > I think we can. mergeable_min_buf_len will just be large.
> >
>
> I meant that we can't just by clearing NETIF_F_SG, we'll need to
change virtio-net a little bit more, for example, the virtnet_set_big_packets
function.
>
Right - for RX, big_packets_num_skbfrags ignores ring size and that's
probably a bug if mtu is very large.
--
MST