Re: [Qemu-devel] [Qemu-discuss] GRO not happening in VM with VxLAN

[Vlad Yasevich <vyasevic@redhat.com>]

On 06/29/2015 01:46 AM, Santosh R wrote:
> All,
> 
>    I am testing VxLAN performance in VM. For this I am using below command
> to bring up the VM.
> # qemu-system-x86_64 -m 4096 -smp 4 -boot c -device
> virtio-net-pci,netdev=tap0,mac=00:11:22:33:44:55 -netdev
> tap,id=tap0,script=no,vhost=on  -drive file=/root/vdisk_rhel65.img &
> 
> This is resulting in lower throughput in VM. On looking further I found
> that GRO is not happing on the tap interface.
> Using tcpdump I could see GRO happeing in physcial nic, vxlan and bridge
> interface. but _not_ on tap interface.

I don't think this is GRO.  GRO  only happens at the lowest possible layer.
For packets coming from external sources, that happens just above the nic
when the packet enters the host for the first time.  From then on, the features
of other devices determine if the large aggregated packet will be segmented
again or not.


> 
> So, I thought to use veth pair instead of the tap interface in VM. What is
> the command to do this?

veth pair will not help with this.  you need a tap or a macvtap to have
VM  talk to host.

> Also,
> 1. Why is rx-checksumming off for tap interface?

because tap doesn't do checksum validation.  it allows lower level devices or
VM to do so.

> 2. Why is GRO not happening with tap interface?
> 

Again.  I don't think it's GRO.  Try capturing traffic at tap and see if you get
large packets (more the 1 mtu long) on the tap.  If not, then someone else is fragmenting
packets and you need to find who.

-vlad

> Pls copy me in all the replies as I am not on the list.
> 
> # brctl show
> bridge name     bridge id               STP enabled     interfaces
> br-vx           8000.323a9146b2d2       no              tap0
>                                                         vxlan0
> # ethtool -k eth35
> Features for eth35:
> rx-checksumming: on
> tx-checksumming: on
>         tx-checksum-ipv4: on
>         tx-checksum-ip-generic: off [fixed]
>         tx-checksum-ipv6: on
>         tx-checksum-fcoe-crc: off [fixed]
>         tx-checksum-sctp: off [fixed]
> scatter-gather: on
>         tx-scatter-gather: on
>         tx-scatter-gather-fraglist: off [fixed]
> tcp-segmentation-offload: on
>         tx-tcp-segmentation: on
>         tx-tcp-ecn-segmentation: on
>         tx-tcp6-segmentation: on
> udp-fragmentation-offload: off [fixed]
> generic-segmentation-offload: on
> generic-receive-offload: on
> large-receive-offload: off [fixed]
> rx-vlan-offload: on
> tx-vlan-offload: on
> ntuple-filters: off [fixed]
> receive-hashing: off [fixed]
> highdma: on
> rx-vlan-filter: off [fixed]
> vlan-challenged: off [fixed]
> tx-lockless: off [fixed]
> netns-local: off [fixed]
> tx-gso-robust: off [fixed]
> tx-fcoe-segmentation: off [fixed]
> tx-gre-segmentation: off [fixed]
> tx-ipip-segmentation: off [fixed]
> tx-sit-segmentation: off [fixed]
> tx-udp_tnl-segmentation: on
> tx-mpls-segmentation: off [fixed]
> fcoe-mtu: off [fixed]
> tx-nocache-copy: off
> loopback: off [fixed]
> rx-fcs: off [fixed]
> rx-all: off [fixed]
> tx-vlan-stag-hw-insert: off [fixed]
> rx-vlan-stag-hw-parse: off [fixed]
> rx-vlan-stag-filter: off [fixed]
> l2-fwd-offload: off [fixed]
> busy-poll: on [fixed]
> 
> # ethtool -k vxlan0
> Features for vxlan0:
> rx-checksumming: on
> tx-checksumming: on
>         tx-checksum-ipv4: off [fixed]
>         tx-checksum-ip-generic: on
>         tx-checksum-ipv6: off [fixed]
>         tx-checksum-fcoe-crc: off [fixed]
>         tx-checksum-sctp: off [fixed]
> scatter-gather: on
>         tx-scatter-gather: on
>         tx-scatter-gather-fraglist: off [fixed]
> tcp-segmentation-offload: on
>         tx-tcp-segmentation: on
>         tx-tcp-ecn-segmentation: on
>         tx-tcp6-segmentation: on
> udp-fragmentation-offload: on
> generic-segmentation-offload: on
> generic-receive-offload: on
> large-receive-offload: off [fixed]
> rx-vlan-offload: off [fixed]
> tx-vlan-offload: on
> ntuple-filters: off [fixed]
> receive-hashing: off [fixed]
> highdma: off [fixed]
> rx-vlan-filter: off [fixed]
> vlan-challenged: off [fixed]
> tx-lockless: on [fixed]
> netns-local: off [fixed]
> tx-gso-robust: off [fixed]
> tx-fcoe-segmentation: off [fixed]
> tx-gre-segmentation: off [fixed]
> tx-ipip-segmentation: off [fixed]
> tx-sit-segmentation: off [fixed]
> tx-udp_tnl-segmentation: off [fixed]
> tx-mpls-segmentation: off [fixed]
> fcoe-mtu: off [fixed]
> tx-nocache-copy: off
> loopback: off [fixed]
> rx-fcs: off [fixed]
> rx-all: off [fixed]
> tx-vlan-stag-hw-insert: on
> rx-vlan-stag-hw-parse: off [fixed]
> rx-vlan-stag-filter: off [fixed]
> l2-fwd-offload: off [fixed]
> busy-poll: off [fixed]
> 
> # ethtool -k tap0
> Features for tap0:
> rx-checksumming: off [fixed]
> tx-checksumming: on
>         tx-checksum-ipv4: off [fixed]
>         tx-checksum-ip-generic: on
>         tx-checksum-ipv6: off [fixed]
>         tx-checksum-fcoe-crc: off [fixed]
>         tx-checksum-sctp: off [fixed]
> scatter-gather: on
>         tx-scatter-gather: on
>         tx-scatter-gather-fraglist: on
> tcp-segmentation-offload: on
>         tx-tcp-segmentation: on
>         tx-tcp-ecn-segmentation: on
>         tx-tcp6-segmentation: on
> udp-fragmentation-offload: off [fixed]
> generic-segmentation-offload: on
> generic-receive-offload: on
> large-receive-offload: off [fixed]
> rx-vlan-offload: off [fixed]
> tx-vlan-offload: on
> ntuple-filters: off [fixed]
> receive-hashing: off [fixed]
> highdma: off [fixed]
> rx-vlan-filter: off [fixed]
> vlan-challenged: off [fixed]
> tx-lockless: off [fixed]
> netns-local: off [fixed]
> tx-gso-robust: off [fixed]
> tx-fcoe-segmentation: off [fixed]
> tx-gre-segmentation: off [fixed]
> tx-ipip-segmentation: off [fixed]
> tx-sit-segmentation: off [fixed]
> tx-udp_tnl-segmentation: off [fixed]
> tx-mpls-segmentation: off [fixed]
> fcoe-mtu: off [fixed]
> tx-nocache-copy: off
> loopback: off [fixed]
> rx-fcs: off [fixed]
> rx-all: off [fixed]
> tx-vlan-stag-hw-insert: on
> rx-vlan-stag-hw-parse: off [fixed]
> rx-vlan-stag-filter: off [fixed]
> l2-fwd-offload: off [fixed]
> busy-poll: off [fixed]
> Thanks
> -Santosh
>