[Openvpn-devel] Linux tun/tap performance issues

[James Yonan]

I believe this has been discussed before, but I noticed recently that a 
Linux-based OpenVPN client (Linux 2.6.24, OpenVPN 2.1.1) spends a lot 
more CPU time in kernel space than in user space.  This is surprising, 
given the fact that all of the CPU-intensive cryptographic operations 
are being done in user space.

Using the 'time' utility on the OpenVPN client, while a wget of a 50MB 
file was done over the VPN, I found that 80% of the CPU time was taken 
by the kernel, and 20% by user space (I should add that the Linux client 
was running as a VM on VMWare Fusion).

I'm wondering if anyone with kernel background has any insights on this. 
 Are there performance bottlenecks in the tun/tap driver?

James