[ovs-discuss] Prioritizing controller and manager (OVSDB) traffic

[Howard Tsai]

Hi,

I would like to prioritize in-band controller and manager (OVSDB) traffic
(on linux.)  The goal is to guarantee that these traffic goes out first,
without rate-limiting other traffic.

I noticed that controller traffic goes out with dscp=48. However, since
Linux do not understand dscp, the traffic is still considered "normal
service" (instead of Minimize-Delay.) It seems to me that setting
SO_PRIORITY to TC_PRIO_INTERACTIVE (defined in
~linux/include/uapi/linux/pkt_sched.h) in lib/socket-util.c:set_dscp (after
setting IP_TOS) could solve this.

Manager traffic seems to do dscp only if remote management is enabled by
"ovs-vsctl set-manager ptcp:6640".  If the remote manager is added by
"ovs-appctl -t ovsdb-server ovsdb-server/add-remote ptcp:6640" (without any
other remotes), the traffic is not dscp marked.  It seems to be a bug to
me.  Also, is one way preferable to the other to add a remote?

The Linux socket priority issue also happens to tunnel traffic (setting tos
in dscp language is not effective.) I suppose another option would be
needed.

I understand prioritization can also be done with a few tc/iptables rules.
 I just hope that the out-of-the-box defaults are in fact effective.

Thanks,
Howard
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