On Mi, 2014-10-22 at 00:44 +0100, Ben Hutchings wrote: > There are several ways that VMs can take advantage of UFO and get the > host to do fragmentation for them: > > drivers/net/macvtap.c: gso_type = SKB_GSO_UDP; > drivers/net/tun.c: skb_shinfo(skb)->gso_type = > SKB_GSO_UDP; > drivers/net/virtio_net.c: skb_shinfo(skb)->gso_type = > SKB_GSO_UDP; > > Our implementation of UFO for IPv6 does: > > fptr = (struct frag_hdr *)(skb_network_header(skb) + > unfrag_ip6hlen); > fptr->nexthdr = nexthdr; > fptr->reserved = 0; > fptr->identification = skb_shinfo(skb)->ip6_frag_id; > > which assumes ip6_frag_id has been set. That's only true if the local > stack constructed the skb; otherwise it appears we get zero. > > This seems to be a regression as a result of: > > commit 916e4cf46d0204806c062c8c6c4d1f633852c5b6 > Author: Hannes Frederic Sowa <[email protected]> > Date: Fri Feb 21 02:55:35 2014 +0100 > > ipv6: reuse ip6_frag_id from ip6_ufo_append_data > > However, that change seems reasonable - we *shouldn't* be choosing IDs > for any other stack. Any paravirt net driver that can use IPv6 UFO > needs to have some way of passing a fragmentation ID to put in > skb_shared_info::ip6_frag_id.
Do we really gain a lot of performance by enabling UFO on those devices or would it make sense to just drop support? It only helps fragmenting large UDP packets, so I don't think it is worth it. Otherwise I agree with Ben, we need to pass a fragmentation id from the host over to the system segmenting the gso frame. Fragmentation ids must be generated by the end system. Hmm... Bye, Hannes _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
