Re: [Xen-users] Understanding netback/netfront GRO/GSO handling

[Kristoffer Egefelt <kristoffer@xxxxxxx>]

>> Is netback/netfront able to send and recieve offloaded packets (64k) via the 
>> physical NICs ?
> 
> netfront/back is certainly capable of transferring packets across the PV
> link without segmentation, and does so by default I believe, that
> feature has been there since time immemorial. (IIRC it arrived either
> just before or early in the old 2.6.18-xen fork days -- so mid 200x's).
> 
> What happens to that SKB once it gets injected into the dom0 network
> stack is a function of the other components on the path to the outside
> world up to and including the specific hardware in the NIC and the
> relevant driver(s) features, but including any
> bridging/forwarding/tunnelling infrastructure along the way.

Good stuff!

>> Specifically I’m experiencing problems when packets egresses a OVS GRE 
>> tunnel - then the packets are segmented to 1500 bytes.
>> Traffic between VMs on the same dom0 maintains the 64k packet size.
>> 
>> As I’m not sure if this is supposed to just work I’m having trouble 
>> identifying if the cause of this could be kernel, NIC drivers, netback, 
>> openvswitch or GRE ...
>> I’m using Debian, kernel 3.13, OVS 2.1, Xen 4.4 and Intel ixgbe drivers.
> 
> Out of those I would be inclined to investigate GRE first, followed by
> openvswitch.
> 
> Removing GRE from your tests would be the logical first step I think.

You are right - its the GRE tunnel - without it it works.
Thanks - I’ll take it further on the openvswitch list.


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxx
http://lists.xen.org/xen-users