[Openvpn-users] Suggestion - improving OpenVPN raw datapump peformance

[Mike Ireton <mike-openvpn@xxxxxxxxxxxxxxxxxx>]

Hi gang,

My application is ethernet bridging, my hardware is cpu limited embedded 
pc's, and I'm wondering about how to improve OpenVPN's peformance. As a 
test, I configured a null openvpn session - no encryption or compression 
- between two wireless nodes, and set up private routing between them. I 
then bridged eth0,tap0 on both sides, and the thruput of openvpn was 
like 700Kb/s with CPU hitting ~ %100.

I then downloaded an example UDP server which used signals and read from 
udp socket and wrote to tap0, or vice versa depending on data 
availabillity. I got about the same peformance out of that.

I then modified the above to become a small multi-threaded udp server 
which simply spawned two threads - a 'read from tap0 and write via udp', 
and a 'receive udp and write to tap0' thread - and after setting up 
bridging going over the wireless interfaces, I was able to get 1.67MB/s 
thru the link (on an ftp download of a large file). One thread sits at ~ 
%70 cpu and the other is at ~ %30 cpu.

Yes my testing methodology is flawed and you probbly couldn't reproduce 
these numbers. But nevertheless, I'm definately seeing about a 2x 
peformance boost in ethernet bridging over udp peformance using this 
technique (vs openvpn with everthing 'off'). I am wondering if 
multithreading just the I/O loop would have a beneficial effect on 
OpenVPN's peformance?? I know that James has written about 
Multithreading previously as a way of lowering latency when key 
exchanges and such, but I've never seen any discussion of raw i/o 
peformance.

By the way, OpenVPN on wireless is great espically when you take 
advantage of the fact that most wireless interfaces can have 
substantially larger MTU sizes, which means that you can do ethernet 
bridging without fragmentation and without mtu issues. That should go 
into a wiki somewhere....

Mike-


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