[ovs-discuss] in-kernel flow table in the datapath

[Masoud Moshref Javadi]

On 4/6/2012 9:20 AM, Jesse Gross wrote:
> On Thu, Apr 5, 2012 at 7:16 PM, Masoud Moshref Javadi
> <masood.moshref.j at gmail.com>  wrote:
>> I have the following experiment and whenever I check ovs-dpctl dump-flows,
>> it gives me less than 7k entries:
>> There are three machines A,B, and C. B runs openvswitch and connect the
>> other two. A and B send 10k packets each second from different flows to the
>> other node. I don't use TCP so there is no ack.  There should be 20k entries
>> there after a second but I get at most 7k and the value changes. It seems
>> that the facet cache cannot hold enough facets, so it replaces them so
>> often. The high cpu usage for ovs-vswitchd process also confirms this claim
>> that the cache cannot hold all entries.
> As I said before, userspace generally tries to keep the number of
> flows installed in the kernel to a few thousand to avoid maintenance
> overhead.  The contents of the kernel flow cache is an implementation
> detail and there's no requirement that it hold everything.  If you
> want to try different values you can set flow-eviction-threshold in
> the config database.

Thank you.
Now suppose that because of this maintenance process and the large 
number of active flows we need to go to the userspace so often and this 
makes high CPU usage. What will happen to the packets if the machine 
cannot handle them with 100% CPU. Is there any DropTail queue there?