[ovs-discuss] Flow table size jump and down

Justin Pettit jpettit at nicira.com
Tue Apr 30 15:30:30 UTC 2013


On Apr 30, 2013, at 1:54 AM, david zhang <david.zhang.ibm at gmail.com> wrote:

> I'd like to know more details about "It can be more aggressive if the flow table becomes large (Are 7000 flows considered as large?)."?

There is a key called "flow-eviction-threshold" described in the ovs-vswitchd.conf.db man page that affects when ovs-vswitchd is more aggressive about expiring flow entries.  Ideally, that value should be the same size as the working set of flows in your switch.  By default, the value is 1000, but we increased it to 2500 in our most recent branches that haven't been released yet.

There is also a flow governor that will prevent creating short-lived kernel flows when it detects a large number of them.  This is to prevent ovs-vswitchd from having to maintain kernel flows that will never be used again.

>  In addition, 2 more questions: 
> (1) Does OVS empty and recreate the kernal flow table at some stage?

The kernel flow table is only built on-demand by ovs-vswitchd when traffic arrives that doesn't match a previous flow.  It's not proactively built or destroyed.

> (2) Can the default flow expire timeout be changed? Like increase to 5mins

No.

--Justin





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