[ovs-dev] [PATCH RFCv4 0/4] AF_XDP netdev support for OVS

[Eelco Chaudron]

On 16 Apr 2019, at 21:55, Ben Pfaff wrote:

> On Mon, Apr 01, 2019 at 03:46:48PM -0700, William Tu wrote:
>> The patch series introduces AF_XDP support for OVS netdev.
>> AF_XDP is a new address family working together with eBPF.
>> In short, a socket with AF_XDP family can receive and send
>> packets from an eBPF/XDP program attached to the netdev.
>> For more details about AF_XDP, please see linux kernel's
>> Documentation/networking/af_xdp.rst
>
> I'm glad to see some more revisions of this series!

I’m planning on reviewing and testing this patch, I’ll try to start 
it this week, or else when I get back from PTO.

> AF_XDP is a faster way to access the existing kernel devices.  If we
> take that point of view, then it would be ideal if AF_XDP were
> automatically used when it was available, instead of adding a new
> network device type.  Is there a reason that this point of view is
> wrong?  That is, when AF_XDP is available, is there a reason not to 
> use
> it?

This needs support by all the ingress and egress ports in the system, 
and currently, there is no API to check this.

There are also features like traffic shaping that will not work. Maybe 
it will be worth adding the table for AF_XDP in 
http://docs.openvswitch.org/en/latest/faq/releases/

> You said that your goal for the next version is to improve performance
> and add optimizations.  Do you think that is important before we merge
> the series?  We can continue to improve performance after it is 
> merged.

The previous patch was rather unstable and I could not get it running 
with the PVP test without crashing. I think this patchset should get 
some proper testing and reviews by others. Especially for all the 
features being marked as supported in the above-mentioned table.

> If we set performance aside, do you have a reason to want to wait to
> merge this?  (I wasn't able to easily apply this series to current
> master, so it'll need at least a rebase before we apply it.  And I 
> have
> only skimmed it, not fully reviewed it.)

Other than the items above, do we really need another datapath? With 
this, we use two or more cores for processing packets. If we poll two 
physical ports it could be 300%, which is a typical use case with 
bonding. What about multiple queue support, does it work? Both in kernel 
and DPDK mode we use multiple queues to distribute the load, with this 
scenario does it double the number of CPUs used? Can we use the poll() 
mode as explained here, 
https://linuxplumbersconf.org/event/2/contributions/99/, and how will it 
work with multiple queues/pmd threads? What about any latency tests, is 
it worse or better than kernel/dpdk? Also with the AF_XDP datapath, 
there is no to leverage hardware offload, like DPDK and TC. And then 
there is the part that it only works on the most recent kernels.

To me looking at this I would say it’s far from being ready to be 
merged into OVS. However, if others decide to go ahead I think it should 
be disabled, not compiled in by default.

> It might make sense to squash all of these into a single patch.  I am
> not sure that they are really distinct conceptually.