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

[Ben Pfaff]

On Tue, Jul 01, 2014 at 04:24:23PM -0700, Howard Tsai wrote:
> 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.

That sounds reasonable.  Will you send a patch?

> 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?

It's not a bug, it just means that "ovsdb-server/add-remote" doesn't
provide a DSCP option.  That's because it's only intended for adding
local controllers (e.g. "unix:", "punix:").  If you want to set other
features, you can add a manager through ovs-vsctl.

> 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.

I think the intent is that you should configure your system to interpret
DSCP appropriately, but I don't know for sure.