Normal CPU usage with a PPP connection

Ted Mittelstaedt tedm at
Wed Feb 27 06:52:32 UTC 2008

> -----Original Message-----
> From: owner-freebsd-questions at
> [mailto:owner-freebsd-questions at]On Behalf Of Nikos
> Vassiliadis
> Sent: Tuesday, February 26, 2008 1:49 AM
> To: freebsd-questions at
> Cc: Dylan Smith
> Subject: Re: Normal CPU usage with a PPP connection
> On Sunday 24 February 2008 14:34:37 Dylan Smith wrote:
> > Hey guys, i'm running 6.3-R with (i think) userland ppp to connect to my
> > ADSL provider over PPPoE.
> > I build a number of graphs(mrtg) for system stats and i am noticing that
> > under heavy load on my ppp connection, that is sustained 150KB/s for an
> > hour or so my cpu usage, based on my graph, hovers around 20% (haven't
> > looked at it in top yet but if there isn't a simple solution/reason for
> > this i will look into what sort of usage it is).
> You should check top and tcpdump, it might be a big number of small
> packets causing the load.
> > The box is a home
> > router/server so at any 1 time isn't doing anything else that i can see
> > would account for this. I also noticed that this usage increase does not
> > occur with traffic coming/going on the inward facing interface, which
> > regularly has transfer speeds around 10 MB/s.
> >
> > I'm running a AMD X2 3800+ with 2GB ram. Is this sort of usage normal?
> Can't really tell if it's normal, but it is known that userland ppp uses
> much resources. I have seen it too using 20% CPU time running on
> a much slower machine(I faintly remember that it was a Pentium
> Celeron at 300MHz) and a much slower(384/128?) ADSL line.
> > Is there something i can do to bring it down?
> Fortunately yes, you could use net/mpd. The CPU load then,
> will probably be near zero for normal traffic, the 150KB/s you
> mention. If a million of small packets arrive at your router the
> load will be higher, nevertheless orders of magnitude lower
> than the load caused by userland ppp.

Or, you can ignore it?  You still have 80% of the CPU doing nothing....


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