[plug] CPU usage with PPP

[Michael Collard]

Just a FYI for anyone else with this problem, its apparently a kernel
bug with the 8139too module and interrupts (not pppoe at all). It is
fixed in > 2.6.13 apparently.

On Wed, 2006-01-18 at 18:34 +0800, Michael Collard wrote:
> I've got my own little gateway/server that handles my pppoe connection
> and provides a number of services. Its a celly 633 with 256Mb RAM. 
> 
> I go to use VoIP today and notice that the quality is crap, to the point
> its dropping out. Hmm, thats odd, that never happens. I start some basic
> troubleshooting. I notice in my log that my server's NIC is having
> timeouts with the following showing up:
> 
> Jan 18 17:44:23 amy kernel: NETDEV WATCHDOG: eth0: transmit timed out
> 
> So I change the port on the switch its going through and that seems to
> have resolved that problem. I go to use the VoIP again and its the same.
> I'm not maxing the 8/1 link... Im doing barely 200K down, maybe 50K up,
> and I use traffic shaping anyway so none of this would impact VoIP. I
> start pinging things and notice high response times to my server and
> anything it NATs. And when I say high on LAN I mean up to and over 20ms.
> 
> That just ain't right especially since other devices respond < .5ms
> where I expect them too. I do a 'top' and notice that pppoe is sitting
> these just as such: 
> 
> 32241 root      25   0  1536  496  428 R 95.1  0.2   3:07.32 pppoe
> 
> So, I am at the stage now where I've killed pppoe and restarted it,
> using the very same config file I've been using for years. Still the
> same. I've killed the firewall (iptables) and shaping (tc) to no avail,
> CPU usage maxes out at about 260Kb/sec on the PPP link. 
> 
> I am almost certain that a reboot will resolve this problem for now, but
> I would rather spend some time, find the cause and fix it properly.
> Anyone have any suggestions on where to start looking?
> 
> There is no APM in use so CPU isn't throttled. Other CPU intensive apps
> (such as MP3 encoding) are fine and normal. It's just PPP as far as I
> can tell right now.
> 
> Cheers
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