title says it all. I have a linux router/vpn server with a core i3 2120 cpu. For vpn connnections to the public internet this isn't an issue, but i'm curious why an iperf test or an ftp download maxes out at around 47-50mbps.

Local tests on the gigabit LAN without the vpn achieves around 947mbps. But over the vpn up stops at around 47. CPU usage by openvpn during a transfer goes up to no more than 18-20%.

motherboard is intel dh77eb, 4gb RAM, arch linux installed on an msata 6gbps drive. it functions as an iptables router for 4 separate networks including the internet.

The CPU usage indicate to all core average or individual thread, which one is it?

i'm just reading from top, the %cpu for the openvpn process

The number of %CPU for particular process is average usage for all threads. You can hit 1 to show all individual threads usage. If individual thread(CPU) is high, that's your CPU power.

Incorrect. The %CPU shown on top is for one processor. If a process is multi-threaded you can see this number jump way above 100%. A value of 20% means it's using 20% of one core of the processor. A dual core CPU like the OP's won't be saturated until you see 200% usage in top (one 200% process, two 100% processes, four 50% processes, etc). Of course this is ignoring hyperthreading though, which changes things a bit.

afaik openvpn is not multithreaded... i could be wrong. in any case I would think that I should be getting more than 47mbps.... is there anything else that could slow it down? i've tested another openvpn setup on a 1.8GHz sempron cpu, and was able to get ~80mbps, so.... somethings up..

What is individual CPU(threads) usage show? Does the openvpn process wait for something else?

figured it out, kind of a facepalm thing. some time ago I had added some tc/iptables classes on the internal interface to limit the speed to around 50mbps. stupid me, didn't make the connection that this would also apply to the tunneling interface, limiting iperf tests done on that interface as well. temporarily removed the tc stuff and speed is around 175-200mpbs now.

oh well. thanks for the help as always folks.