[ovs-discuss] ovs-vswitchd port limit with OpenStack

Ben Pfaff blp at ovn.org
Tue Apr 30 23:50:48 UTC 2019


On Fri, Apr 26, 2019 at 11:52:22AM -0500, William Konitzer wrote:
> I'm reading
> (http://www.openvswitch.org/support/dist-docs/ovs-vswitchd.8.txt
> section LIMITS) and it says "Performance will degrade beyond 1,024
> ports per bridge due to fixed hash table sizing.” Do we have a little
> more info on what that means and what to expect for less experienced
> users like myself?

I think that this comment is now obsolete.  There was a fairly recent
change that should have reduced the cost of a port.  The kernel hash
table is still fixed in size but I don't think it's accessed on any fast
path so I think in practice it doesn't matter.

> The background here is we’re working with OpenStack and seeing
> performance issues when lots of networks are created.. Once we have
> more than about 1500 ports on the br-int on a gateway node it seems to
> take a long time to add new ports.
> 
> I’m trying to quickly determine if we have a config issue, an
> Openstack issue or whether we’re hitting some sort of OVS limit as
> described. It seems to me that 1500 ports isn’t that many, but I’m not
> sure what sort of performance degradation I should be expecting above
> 1024 ports. The gateway node is so lightly loaded that I’d prefer to
> be able to handle a lot more networks on it before deploying another
> one.

Are you adding ports one at a time with ovs-vsctl?  If you can add them
in a batch, it will perform better.  I guess we could also add a "daemon
mode" like ovn-nbctl, which would help a good deal too.


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