Pi4 OpenVPN server performance is terrible

[Mazvydas]

I was excited to utilize the 1gbps LAN the Pi4 has as I have a 1gbps up/down connection, but was shocked at how bad OpenPVN performs.

I did tests on my phone with the android app on my phone, and at best I could muster was ~20Mbps down ~10mbps up. Without VPN I got stable 100Mbps up/down. It was even worse on 4G LTE - ~5-10Mbps down, ~1-5Mbps up with VPN enabled, and around ~50MBps up/down with VPN disabled.

I checked htop during speedtests, the cpu utilization was ~25%, 3gb of ram free, nothing else transferring to/from the Pi at the time. I at one point set cipher and auth to none in server.conf for OpenVPN and still wouldn't get faster speeds.

I can download files off the pi at 100mb/s from outside my LAN, so this ~20Mbps limit (2-3mb/s) is definitely not related to my home networking/router.

What gives? Any ideas?