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From: Luigi Rizzo <rizzo@iet.unipi.it>
To: Evgenii Davidov <dado@korolev-net.ru>
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Cc: freebsd-ipfw@freebsd.org
Subject: Re: dummynet: waking up pipe
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On Fri, Jan 22, 2010 at 04:35:35PM +0300, Evgenii Davidov wrote:
...
> > > > my problem is that dummynet cpu usage jumps from 0 to 99%:
> > > > 
> > > >    33 root        1 -68    -     0K     8K -       1 512.6H 86.18% dummynet
> > > >    33 root        1 -68    -     0K     8K -       1 512.6H 85.89% dummynet
> > > >    33 root        1 -68    -     0K     8K -       1 512.6H 88.28% dummynet
> > > >    33 root        1 -68    -     0K     8K -       0 512.6H 78.17% dummynet
> > > >    33 root        1 -68    -     0K     8K -       0 512.6H  0.88% dummynet
> > > >    33 root        1 -68    -     0K     8K -       1 512.6H  0.10% dummynet
> > > >    33 root        1 -68    -     0K     8K -       1 512.7H  0.00% dummynet
> > > >    33 root        1 -68    -     0K     8K -       1 512.7H  0.10% dummynet
> > 
> > i am not too clear on why this happens -- there shuold be only
> > one instance of the dummynet thread, not 8 as in your case.
> 
> no-no, one instance, it's a grep of a top log

ok then it's rather normal -- the task wakes up every millisecond and
it might have hundreds of packets to send at once, especially when
the machine is heavily loaded as in your case.