[ovs-discuss] prioritizing latency-sensitive traffic

[O Mahony, Billy]

Hi Ben, Darrell,

It sounds like the general feeling is that any kind of tc pre-processing is not worth it and the existing egress queing/QoS facilities should suffice. 

Thanks for your comments.

/Billy



> -----Original Message-----
> From: Ben Pfaff [mailto:blp at ovn.org]
> Sent: Thursday, April 13, 2017 7:47 PM
> To: O Mahony, Billy <billy.o.mahony at intel.com>
> Cc: ovs-discuss at openvswitch.org
> Subject: Re: [ovs-discuss] prioritizing latency-sensitive traffic
> 
> I don't know how much more OVS can contribute to this than it already does.
> By the time that OVS has classified a packet to the extent that is necessary to
> determine that it should be handled with a high priority, OVS has already
> done most of the work that it does on a packet.  
[[BO'M]] I'm investigating how I could go about classifying packets before the main 
The work to transmit the
> packet is not part of OVS's job, it is the job of the driver, and at most OVS can
> mark the packet with a priority or a queue.  OVS can already do that.  So the
> usual answer is that it's a matter of configuring QoS in the driver to do what
> the user wants.
> 
> On Mon, Apr 10, 2017 at 09:30:12AM +0000, O Mahony, Billy wrote:
> > Hi Everybody,
> >
> > I just wanted to reflag this discussion below about possible methods of
> how to prioritize certain types of traffic handled by OVS.
> >
> > By prioritize I mean either or both of:
> > a) 'priority' packets are sent to their destination port faster than
> > other packets
> > b) in an overloaded situation the switch drops non-prioritized packets
> rather than prioritized packets.
> >
> > Also just to be clear I am discussing kernel ovs here. Also I'm looking at
> doing this without writing new code - ie is it possible and if so how is it
> configured using existing OVS.
> >
> > Thanks again,
> > Billy.
> >
> > > -----Original Message-----
> > > From: ovs-discuss-bounces at openvswitch.org [mailto:ovs-discuss-
> > > bounces at openvswitch.org] On Behalf Of O Mahony, Billy
> > > Sent: Friday, November 25, 2016 5:04 PM
> > > To: ovs-discuss at openvswitch.org
> > > Subject: [ovs-discuss] prioritizing latency-sensitive traffic
> > >
> > > Hi,
> > >
> > > I have been performing tests investigating latency profiles of
> > > low-bandwidth time-sensitive traffic when the system is busy with
> 'normal' traffic.
> > > Unsurprisingly the latency-sensitive traffic is affected by the
> > > normal traffic and has basically the same latency profile as the normal
> traffic.
> > >
> > > I would like to be able to perform prioritization of traffic as some
> > > protocols such as PTP would benefit greatly from having it's packets 'jump
> the queue'.
> > >
> > > From skimming the documentation it looks that ingress QoS offers
> > > only policing (rate-limiting). Is this actually the case or maybe
> > > I'm not looking in the right place?
> > >
> > > But if so, I am looking at some alternatives:
> > >
> > > a) create two separate egress ports and have PTP listen on one port,
> > > everything else listen on the other port and use normal forwarding
> > > rules to send PTP traffic incoming from eth0 to it's own port. Something
> like:
> > >
> > >  other apps          ptp_daemon
> > >       +               +
> > >       +               +
> > >    if_norm         if_ptp
> > >        +            +
> > >        |            |
> > >        |            |
> > >       ++------------++
> > >       |              |
> > >       |    ovs       |
> > >       |              |
> > >       +-----+--------+
> > >             |
> > >             +
> > >           eth0
> > >
> > > b) create prioritized queues on a port and use match and actions
> > > such as
> > > set_queue(queue) and enqueue(port, queue) on ingress traffic to
> > > forward the PTP traffic to the higher priority queue. However I
> > > think queue priority for this case only relates to which queue get
> > > to consume the bandwidth of the port first and not about changing
> > > the order in which the packets egress the port.
> > >
> > > c) Or perhaps I can re-use tc PRIO or CBQ qdiscs by passing all
> > > traffic to tc first before ovs?
> > >
> > >  other apps
> > >       |
> > >       |
> > >    if_norm
> > >        +
> > >        |
> > >        |
> > >       +--------------+
> > >       |              |
> > >       |    ovs       |
> > >       |              |
> > >       +-----+--------+
> > >             |
> > >             |
> > >             tc ----- if_ptp ---- ptp_daemon
> > >             +
> > >           eth0
> > >
> > > Any thoughts, ideas or clarifications most welcome.
> > >
> > > Thanks,
> > > Billy.
> > >
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