Hi Maxime, > -----Original Message----- > From: Maxime Coquelin [mailto:maxime.coque...@redhat.com] > Sent: Wednesday, December 6, 2017 4:34 PM > To: Hu, Jiayu <jiayu...@intel.com>; dev@dpdk.org > Cc: y...@fridaylinux.org; Tan, Jianfeng <jianfeng....@intel.com> > Subject: Re: [dpdk-dev] [PATCH] vhost: support Generic Segmentation > Offload > > Hi Jiayu, > > On 11/28/2017 06:28 AM, Jiayu Hu wrote: > > In virtio, Generic Segmentation Offload (GSO) is the feature for the > > backend, which means the backend can receive packets with any GSO > > type. > > > > Virtio-net enables the GSO feature by default, and vhost-net supports it. > > To make live migration from vhost-net to vhost-user possible, this patch > > enables GSO for vhost-user. > > Please note that the application relying on Vhost library may disable > some features, breaking the migration from vhost-net to vhost-user even > if all features are supported in the vhost-user lib. > > For example, ovs-dpdk disables the following features: > err = rte_vhost_driver_disable_features(dev->vhost_id, > 1ULL << VIRTIO_NET_F_HOST_TSO4 > | 1ULL << VIRTIO_NET_F_HOST_TSO6 > | 1ULL << VIRTIO_NET_F_CSUM); > > > > Signed-off-by: Jiayu Hu <jiayu...@intel.com> > > --- > > lib/librte_vhost/vhost.h | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h > > index 1cc81c1..04f54cb 100644 > > --- a/lib/librte_vhost/vhost.h > > +++ b/lib/librte_vhost/vhost.h > > @@ -204,6 +204,7 @@ struct vhost_msg { > > (1ULL << VIRTIO_F_VERSION_1) | \ > > (1ULL << VHOST_F_LOG_ALL) | \ > > (1ULL << > VHOST_USER_F_PROTOCOL_FEATURES) | \ > > + (1ULL << VIRTIO_NET_F_GSO) | \ > > This feature is also enabled by default in QEMU, and seems also to be > acked by default in the virtio-net kernel driver. > > Does it have an impact on performance? Be it good or bad. > > How to test it?
VIRTIO_NET_F_GSO is the combination of all backend GSO types, like VIRTIO_NET_F_HOST_UFO and VIRTIO_NET_F_HOST_ECN. Supporting VIRTIO_NET_F_GSO equals to supporting all backend GSO types. In the virtio-net driver, VIRTIO_NET_F_GSO influences the offloading abilities of virtio-net devices. When VIRTIO_NET_F_GSO is negotiated, the virtio-net device has TSO(_ECN) and UFO turned on by default. It equals to enabling "host_ufo", "host_tso4/6" and "host_ecn". About the performance, when VIRTIO_NET_F_GSO is enabled, the device can send large TCP/UDP packets (exceeding MTU) to the backend. Large packets can reduce the per-packet overhead. Therefore, I think it's good for performance. We can test this feature with the following configuration: Environment: - one server with two physical interfaces (p1 and p2). - p1 and p2 are connected physically. p1 is assigned to DPDK and p2 is to kernel. Steps: - launch testpmd with p1 and one vhost-user port - launching qemu with command "gso=on, csum=on". In the VM, you can see TSO_ECN and UFO of the virtio-net port are enabled by default. - Run "iperf -u -s ..." on p2 - run "iperf -u -c ... -l 7000B" in the VM. Therefore, iperf client will send large UDP packets - "show port xstats all" in testpmd. You can see the vhost-user port receives large UDP packets from the frontend. You can also use the above steps to test the vhost-user host_ufo feature. Thanks, Jiayu > > > (1ULL << VIRTIO_NET_F_HOST_TSO4) | \ > > (1ULL << VIRTIO_NET_F_HOST_TSO6) | \ > > (1ULL << VIRTIO_NET_F_CSUM) | \ > > > > Thanks, > Maxime
