Since I frequently use public WiFi hotspots I run an OpenVPN server on my Ubuntu 14.04 LTS linode to keep my connection secure. The VPN was working wonderfully until yesterday when download speeds became very slow.

I tried changing MTU, compression settings and other parameters in OpenVPN config but the slowness continued. It took me some time to figure out that the only thing I changed was rebooting my linode the night before it stopped working.

I do not know when the latest kernel was published but going back to the previous kernel fixed the problem. I confirmed it by temporarily going back to the newest and seeing that the connection slowness returns.

Looks like it's a kernel bug: https://bugzilla.kernel.org/show_bug.cgi?id=74051

The fix got committed for 3.15 (https://github.com/torvalds/linux/commi ... 7375a492bf), but I'm unsure about 3.14. I saw one reference suggesting it was merged into 3.14.2, but I didn't see it in the 3.14.2 release announcement, nor does it seem applied to the git tree (unless it was a distribution-specific merge).

So it looks like it's probably best to avoid 3.14 at least for the time being if using tun devices.

-- David

May thanks, db3l... I've wasted at least 12 hours trying to figure this out - I came here to ask for help, fortunately I did a search first and saw your post - bingo trouble solved... thanks.

The fix for this isn't in 3.14.2 or 3.14.3. I expect it'll be in 3.14.4, at which point we'll roll a new kernel of that version. If by some stroke of insanity they don't put the fix in 3.14.4, I expect I'll be manually applying the patch and releasing 3.14.4+

- Les

I just updated to the latest kernel (3.14.4-x86_64-linode40) and verified that TUN performance has been restored back to normal. Thanks