[ovs-discuss] H/w offloading list for OVS 1.2.2

[Dave Whitla]

Its true I may have assumed wider implications than I should based upon the documentation combined with having seen this now on several different vendor NICs.
So far with the vast array of varied hardware at my disposal I have yet to see it not occur with my specific networking configuration.
I was first interested in Open Virtual Switch as a replacement for linux bridging for this exact reason. There are several threads on Citrix' XenServer fora relating to the issue - one suggesting that OVS would solve the problem.
It turned out that after replacing linux bridge config on my cluster nodes with OVS the problem was not resolved. But OVS supplied plenty of other benefits justifying the change.
Specifically I am forced in my environment to mix trunked and VLAN (fake bridge) ports on each switch due to having to allow certain guests to manage their own access to VLANs on the switch.
I fully expected this to be problematic with respect to offloading certain functions to hardware. I can't recall OTTOMH where I saw it, but in relation to this issue I saw posts containing kernel source extracts showing why it occurs, and asserting that its systemic to the Linux networking stack.

If it would help to investigate I can provide steps to replicate using my stack which consists of:

Debian Wheezy
Linux kernel 3.1.1
Xen 4.1.2
OVS 1.2.2 (patched for kernel 3.1 compatibility)

Incidentally I am using 1.2.2 from the Wheezy distribution because it is (last I checked) the latest available from our repos. It was less effort to patch that than build my own 1.3 distribution packages only to have them conflict when 1.3 reaches the Debian repos.

Dave




On 16/12/2011, at 11:52 AM, Jesse Gross wrote:

> On Thu, Dec 15, 2011 at 5:31 PM, Dave Whitla <dave.whitla at ocean.net.au> wrote:
>> Well the Xen documentation specifically mentions it. The Debian Xen packages specifically create network config within VMs for it - as well as documenting the same.
>> And I have personally experienced it - the last time causing me me a couple of days of head scratching until I figured out how to disable hardware tx checksum offload on F5's LTM VE.
> 
> I know of a few situations where drivers have difficulty with vlan
> tags and offloads (primarily around trunking or with older versions of
> Linux).  However, to make a blanket statement that it doesn't work is
> misleading (and I do see that the documentation says that, although I
> believe that it is out of date).