[dpdk-users] OVS-DPDK performance raises when stress is running on the same core

[Dawid Deja <dawidd@telco.com>]

Hello,

I was testing how the OVS-DPDK will perform when putted into cgroup. To
my surprise, the performance raises once ovs-vswitchd process was able
to consume only 50% of CPU. Here's what I've done:

1. I have configured OVS to use dpdk and to run on core no 2;
2. I have created bridge with datapath_type=netdev, added a dpdk
interface to it and connected a VM to this bridge via vhostuser port;
3. I have created new cgroup, set the cpu.shares to 512 and added the
pid of ovs-vswitchd process to tasks;

At that point, I measured the throuhput from the VM, via the dpdk
interface to the external machine using iperf3:

iperf3 -c 192.168.0.3 -M 104

The bandwith was around 40Mb/s. After that:

4. I have started stress process to stress one core (# stress -c 1);
5. I have added the stress process to cgroup created in point 3;
6. Using taskset, I've put stress on same core as ovs-vswitchd;

Then I run the iperf3 again, with same command. The bandwith was around
100 Mb/s.Can this be explained somehow?

The tests were run on host with Atom CPU (Intel(R) Atom(TM)
CPU  C2758  @ 2.40GHz).

Thanks,
Dawid Deja