[ovs-dev] Status of Open vSwitch with DPDK

Gray, Mark D mark.d.gray at intel.com
Fri Aug 14 16:04:40 UTC 2015

Hi Daniele,

Thanks for starting this conversation. It is a good list :) I have crossed-posted this
to dpdk.org as I feel that some of the points could be interesting to that community
as they are related to how DPDK is used.

How do "users" of OVS with DPDK feel about this list? Does anyone disagree or
does anyone have any additions? What are your experiences?

> There has been some discussion lately about the status of the Open vSwitch
> port to DPDK.  While part of the code has been tested for quite some time,
> I think we can agree that there are a few rough spots that prevent it from
> being easily deployed and used.
> I was hoping to get some feedback from the community about those rough
> spots,
> i.e. areas where OVS+DPDK can/needs to improve to become more
> "production
> ready" and user-friendly.
> - PMD threads and queues management: the code has shown several bugs
> and
> the
>   netdev interfaces don't seem up to the job anymore.

You had a few ideas about how to refactor this before but I was concerned 
about the effect it would have on throughput. I can't find the thread. 

Do you have some further ideas about how to achieve this?

>   There's a lot of margin of improvement: we could factor out the code from
>   dpif-netdev, add configuration parameters for advanced users, and figure
> out
>   a way to add unit tests.

I think this is a general issue with both the kernel datapath (and netdevs)
and the userspace datapath. There isn't much unit testing (or testing) outside
of the slow path. 

>   Related to this, the system should be as fast as possible out-of-the-box,
>   without requiring too much tuning.

This is a good point. I think the kernel datapath has a similar issue. You can
get a certain level of performance without compiling with -Ofast or
pinning threads but you will (even with the kernel datapath) get better
performance if you pin threads (and possibly compile differently). I guess
it is more visible with the dpdk datapath as performance is one of the key
values. It is also more detrimental to the performance if you don't set it
up correctly.

Perhaps we could provide scripts to help do this?

I think this is also interesting to the DPDK community. There is 
knowledge required when running DPDK enabled apps to
get good performance: core pinning is one thing that comes to mind.

> - Userspace tunneling: while the code has been there for quite some time it
>   hasn't received the level of testing that the Linux kernel datapath
> tunneling
>   has.

Again, there is a lack of test infrastructure in general for OVS. vsperf is a good
start, and it would be great to see more people use and contribute to it!

> - Documentation: other than a step by step tutorial,  it cannot be said
> that
>   DPDK is a first class citizen in the OVS documentation.  Manpages could
> be
>   improved.

Easily done. The INSTALL guide is pretty good but the structure could be better. 
There is also a lack of manpages. Good point.

> - Vhost: the code has not received the level of testing of the kernel
> vhost.
>   Another doubt shared by some developers is whether we should keep
>   vhost-cuse, given its relatively low ease of use and the overlapping with
>   the far more standard vhost-user.

vhost-cuse is required for older versions of qemu. I'm aware of some companies
using it as they are restricted to an older version of qemu. I think it is deprecated
at the moment? Is there a notice to that effect? We just need a plan for when to
remove it and make sure that plan is clear?

> - Interface management and naming: interfaces must be manually removed
> from
>   the kernel drivers.
>   We still don't have an easy way to identify them. Ideas are welcome: how
> can
>   we make this user friendly?  Is there a better solution on the DPDK side?

This is a tough one and is interesting to the DPDK community.  The basic issue
here is that users are more familiar with linux interfaces and linux naming

"ovs-vsctl add-port bro eth0" makes a lot more sense than

"dpdk_nic_bind -b igb_uio <pci_id>", then check the order that the ports
are enumerated and then run "ovs-vsctl add-port br0 dpdkN".

I can think of ways to do this with physical NICs. For example,
you could reference the port by the linux name and when you try to add it, OVS
could unbind from the kernel module and bind it to igb_uio?

However, I am not sure how you would do it with virtual nics as there is not
even a real device.

I think a general solution from the dpdk community would be really helpful here.
>   How are DPDK interfaces handled by linux distributions? I've heard about
>   ongoing work for RHEL and Ubuntu, it would be interesting to coordinate.
> - Insight into the system and debuggability: nothing beats tcpdump for the
>   kernel datapath.  Can something similar be done for the userspace
> datapath?

Yeah, this would be useful. I have my own way of dealing with this. For example,
you could dump from the LOCAL port on a NORMAL bridge or add a rule to 
mirror a flow to another port but I feel there could be a better way to do this in
DPDK. I have recently heard that the DPDK team do something with a pcap pmd
to help with debugging. A more general approach from dpdk would help a lot.
> - Consistency of the tools: some commands are slightly different for the
>   userspace/kernel datapath.  Ideally there shouldn't be any difference.

Yeah, there are some things that could be changed. DPDK just works differently but
the benefits are significant :)

We need to mount hugepages, bind nics to igb_uio, etc

With a lot of this stuff, maybe the DPDK community's tools don't need to emulate
the linux networking tools exactly. Maybe over time as the DPDK community
and user-base expands, people will become more familiar with the tools, processes, etc
and this will be less of an issue?

> - Packaging: how should the distributions package DPDK and OVS? Should
> there
>   only be a single build to handle both the kernel and the userspace
> datapath,
>   eventually dynamically linked to DPDK?

Yeah. Do we need to start with dpdk if we have compiled with DPDK support???
> - Benchmarks: we often rely on extremely simple flow tables with single
> flow
>   traffic to evaluate the effect of a change.  That may be ok during
>   development, but OVS with the kernel datapath has been tested in
> different
>   scenarios with more complicated flow tables and even with hostile traffic
>   patterns.
>   Efforts in this sense are being made, like the vsperf project, or even
> the
>   simple ovs-pipeline.py

vsperf will really help this.

> I would appreciate feedback on the above points, not (only) in terms of
> solutions, but in terms of requirements that you feel are important for our
> system to be considered ready.
> Cheers,
> Daniele

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