[ovs-discuss] Multiple dpdk-netdev datapath with OVS 2.9

[Ben Pfaff]

It's mostly for historical reasons.

We do try to document in ovs-vswitchd(8) that the user should not manage
datapaths themselves:

       ovs-vswitchd does all the necessary management of Open vSwitch
       datapaths itself.  Thus, external tools, such ovs-dpctl(8), are
       not needed for managing datapaths in conjunction with
       ovs-vswitchd, and their use to modify datapaths when ovs-vswitchd
       is running can interfere with its operation.  (ovs-dpctl may
       still be useful for diagnostics.)

I guess that the wording should be updated to reflect the "ovs-appctl"
interface too.

I sent a patch to improve the docs here:
https://patchwork.ozlabs.org/patch/908532/

On Thu, May 03, 2018 at 06:44:43PM +0500, alp.arslan at xflowresearch.com wrote:
> If "ovs-vswitchd" manages the data paths, why does it have a utility that
> lets me create more of them. And when I create them I cannot use them. I am
> stuck in a loop :) . 
> 
> -----Original Message-----
> From: Ben Pfaff [mailto:blp at ovn.org] 
> Sent: Thursday, May 3, 2018 4:41 PM
> To: alp.arslan at xflowresearch.com
> Cc: discuss at openvswitch.org
> Subject: Re: [ovs-discuss] Multiple dpdk-netdev datapath with OVS 2.9
> 
> On Wed, May 02, 2018 at 10:02:04PM +0500, alp.arslan at xflowresearch.com
> wrote:
> > I am trying to create multiple dpdk-netdev based data paths with OVS 
> > 2.9 and DPDK 16.11 running on CentOS 7.4. I am able to create multiple 
> > data paths using "ovs-appctl dpctl/add-dp netdev at netdev1" and I can 
> > see a new data path created with "ovs-appctl dpctl/show". However I 
> > cannot add any interfaces (dpdk or otherwise), and I cannot set this 
> > data path as datapath_type to any bridge.
> 
> That's not useful or a good idea.  ovs-vswitchd manages datapaths itself.
> Adding and removing them yourself will not help.
> 
> > Just a precap to why I am trying to do this, I am working with a lot 
> > of OVS OpenFlow rules (around 0.5 million) matching layer 3 and layer 
> > 4 fields. The incoming traffic is more than 40G (4 x10G Intel x520s), 
> > and has multiple parallel flows (over a million IPs). With this the 
> > OVS performance decreases and each port is forwarding only around 250 
> > Mb/s. I am using multiple RX queues (4-6), with single RX queue it 
> > drops to 70 Mb/s. Now if I shutdown three 10G interfaces, an 
> > interesting thing happen, and OVS starts forwarding over 7Gb/s for 
> > that single interface. That got me thinking, maybe the reason for low 
> > performance is 40 G traffic hitting a single bridges flow tables, how 
> > about creating multiple bridges with multiple flow tables. With this 
> > setup the situation remained same, and now the only common thing 
> > between the
> > 4 interfaces is the data path. They are not sharing anything else. 
> > They are polled by dedicated vCPUs, and they are in different tables.
> > 
> >  
> > 
> > Can anyone explain this bizarre scenario of why the OVS is able to 
> > forward more traffic over single interface polled by 6 vCPUs, compared 
> > to 4 interfaces polled by 24 vCPUs.
> > 
> > Also is there a way to create multiple data paths and remove this 
> > dependency also.
> 
> You can create multiple bridges with "ovs-vsctl add-br".  OVS doesn't use
> multiple datapaths.
> 
> Maybe someone who understands the DPDK port better can suggest some reason
> for the performance characteristics that you see.
>