[ovs-discuss] prioritizing latency-sensitive traffic

[Ben Pfaff]

Thanks for letting us know.  I'm happy to continue the conversation if
there are interesting ideas; it's a frustrating situation, frankly, and
I'd love to hear creative approaches.

On Tue, Apr 18, 2017 at 10:01:28AM +0000, O Mahony, Billy wrote:
> 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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