Hi, I read some kernel source. My basic understanding is that, in net/8021q/vlan_dev.c, vlan_dev_init, the dev->features of vconfig created interface is defined to be dev->features |= real_dev->features & real_dev->vlan_features; However, in drivers/net/virtio_net.c, vlan_features are never set (I will assume it would be 0). So, dev->features will be 0 for the ethX.vid interface. I verify it using ethtool -k on each KVM. # ethtool -k eth0 shows that rx/tx csum, sg, tso, gso are on # ethtool -k eth0.3003 all offloading features are off. I think that is why TSO is never enabled when running large package traffic between two vlan interfaces of different KVMs. I also took a look at VMware's pv implementation, which is drivers/net/vmxnet3/vmxnet3_drv.c, they have enable dev->vlan_features when probing, by netdev->vlan_features = netdev->features; I was wondering why vlan_features was not defined in virtio_net. Is it a BUG? Or, it is due to some constraints? Could any explain that? Thanks, -D On Thu, Feb 25, 2010 at 6:30 PM, David V. Cloud <david.v.cloud@xxxxxxxxx> wrote: > Hi all, > I have been deploying two KVMs on my Debian testing box. Two KVMs each > use one tap device connecting to the host. > > When I > doing netperf with large package size from KVM2 (tap1) to KVM1 (tap0) > using ethX on them, I could verify that TSO did happened by > # tcpdump -nt -i tap1 > I can see messages like, > IP 192.168.101.2.39994 > 192.168.101.1.41316: Flags [P.], seq > 7912865:7918657, ack 0, win 92, options [nop,nop,TS val 874151 ecr > 874803], length 5792 > > So, according the 'length', skb didn't get segmented. > > However, When I > (1) setup VLAN using vconfig on KVM2, KVM1, and got two new interface > eth1.3003, eth0.3003 on both machines. > (2) netperf between two new interface, TSO no longer showed up, > # tcpdump -nt -i tap1 > I only got, > vlan 3003, p 0, IP 10.214.10.2.42324 > 10.214.10.1.56460: Flags [P.], > seq 2127976:2129424, ack 1, win 92, options [nop,nop,TS val 926034 ecr > 926686], length 1448 > > So, all the large packages get segmented in virtio (is that right?) > > My KVM command line options are, > kvm -hda $IMG -m 768 -net nic,model=virtio,macaddr=52:54:00:12:34:56 > -net tap,ifname=$TAP,script=no > > > > My question is whether it is the expected behavior? Can VLAN tagging > coexist with TSO in virtio_net driver? > If this is not desired result. Any hint for fixing the problem? > > Thanks > -D > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
