[ovs-discuss] Packet loss with RFC2544 based tests

[Justin Pettit]

> On Jul 25, 2016, at 9:52 AM, Chiappero, Marco <marco.chiappero at intel.com> wrote:
> 
> Hello everyone,
>  
> I’m currently carrying out RFC2544 based tests on a server running hundreds of applications which forward back a matching number of traffic flows generated by a HW traffic generator. These applications are running in Linux containers, bridged altogether by a single OvS bridge instance (using the DP kernel module).
>  
> However a significant packet loss happens at the very beginning of every run beyond a certain line rate, somehow invalidating the tests. When slowly increasing the load by hand, from a minimum to the target rate, no such loss can be seen. Suspecting an initial delay due to the need to fill the microflow cache, I tried increasing the number of handler threads and their priority without success.
>  
> Is this the expected behavior or could it be related to misconfiguration? What are the best practices for testing OvS, are there any better approaches?

Yes, this is known/expected behavior.  Those tests were designed for hardware switches, which don't generally have caches on their fastpath that need to be heated up.  I think this has been previously discussed on the mailing lists, so you could search there.  You may want to check out this presentation from the 2015 OVS conference:

	https://www.youtube.com/watch?v=ZILwdFLy6c4

Here are the accompanying slides:

	http://openvswitch.org/support/ovscon2015/17/1050-abidi.pptx

As they suggest, you may try increasing the max-idle value to something closer to 50000.

This seems to follow some of the tuning suggestions done by other folks at Intel when testing the DPDK port:

    https://download.01.org/packet-processing/ONPS1.5/Intel_ONP_Server_Release_1.5_Performance_Test_Report_Rev1.2.pdf

Let us know what you find out.  It's probably worth adding a FAQ entry.

--Justin