Client slow when cpu busy (i.e youtube)

justmoi

Hello,
on my coreduo T2250 1.7Ghz running W7-64, openvpn 2.2, I noticed that network speed is severely affected by cpu usage, most noticeably seen when streaming videos (youtube). It is very easy to reproduce in my case:
www.youtube.com/my_speed
I display the video, switch to 720p, bitrate is around 1 to 2Mb/s max (60% cpu used). If I pause the video or buffer gets empty and refills, bitrate jumps to 5-10Mb/s (my connection top speed). With an l2tp/ipsec vpn or no vpn at all, I can get top speed while playing, so I am confused as to why openvpn is so affected by cpu usage.
I tried disabling lzo and even setting cipher to none, same result, so it may have something to do with the TAP driver?
Any hint on how to diagnose this issue welcome.
Martin

janjust

the good news is:

I can reproduce this quite easily, both on windows 7 and XP (though the XP was a VM); I have a 14 Mbps home DSL connection ; when streaming video the youtube numbers drop from 14 Mbps to 5 Mbps ; pause the video and the number climbs back up to 14 Mbps.

The exact same test on the exact same i5-560M laptop running Linux does not show this drop in performance.

the bad news is: I have no clue what can be done about this; clearly there are issues in the tap-win32 adapter, which seem to have gotten worse with Vista/7, but it is not clear how they csan be resolved. I've asked the developers , but so far no answers.

justmoi

Thanks a lot for your informative reply. I will wait for more news if the devs manage to find out what is going on.

justmoi

ping? As my provider decided that youtube is too expensive and prefer rate-limiting rather than setting up more pipes, I need to use OpenVPN to bypass the restriction.

userito

Have same slow down winth Win7(point) + WinXP(point). (0,5 mbps..1,5mbps)
When change env. to WinXP + WinXP file transfer speeds up to 17,5mbps .. 18,500 mbps!!!!!!!!

Have used iperf (sourceforge.net) for testing.

userito

Hello have same trouble with Win7 + WinXP ( 1,5 mbps when long test about 120 sec. Sometimes it starts with 10mbps then slow down to 0,5mbps.

Change to XP + XP it works at about 18mbps (other comp maybe CPU performed better+XP)

Then shut down at Win7 computer firewall and get 10mbps.

I think win7 firewall slows down the openwpn connection.