On Mon, Apr 17, 2023 at 07:33:58AM +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. > > > > Good point. > > > > > > > > > * 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. > > > > So, what do you think, we should fix virtio-net to work with smaller rings? we should fail probe? > > I think that since this never came up until now, there is no big demand to such small rings. The worry is that once we start failing probe there's just a tiny chance hosts begin to rely on us failing probe then we won't be able to fix it. So it depends on the size of the patch I think. So far it seems small enough that wasting code on failing probe isn't worth it. -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
