Cbench test - ODL throughput drops by increasing the number of switches

ODL version: Beryllium-SR2
Benchmarking Tool: Cbench

I conducted a throughput test using cbench on ODL and ONOS. I noticed there's a huge gap between the numbers that I get from these two controllers. (ONOS throughout is almost x10 and latency is almost x2 better than ODL overall)

When scaling up the number of switches from 1 to 8 throughout gets better (the maximum observed throughput is with 8 switches). However, throughput drops when increasing the number of switches more than 8.

Following above observation I figured ONOS and ODL using the same I/O plugin library (Netty) and even ODL uses a newer version. Using more CPU threads, assign more memory, and tweaking Java heap size does not change the numbers that much (Less than 5%)

Considering the fact these two controllers using the same I/O plugin (which is being tested in cbench throughput test), and allocating more resources to ODL does not help to improve the performance, I'm suspecting maybe there's a bug in ODL code.

Cheers,
Mohamad