CPU utilization calculation broken with SCHED_ULE and dummynet

Stefan Ehmann shoesoft at gmx.net
Fri Oct 31 10:33:15 PDT 2008

Already posted this earlier this month and filed as kern/128177.

Short summary: top/ps displays 0% instead of 100% CPU usage for CPU-intensive 
processes. single-threaded process on single-CPU i386 machine.

I think this also negatively effects scheduling decisions but haven't found a 
good way to test this.

I did some more investigations today:

The problem only occurs when the dummynet module is loaded. If I unload the 
module everything seems fine. It's enough if the module is loaded, no rules 
involving dummynet are needed.

If I revert (SVN rev 183294) the problem is gone.

Already noted earlier:
I don't see the problem in CURRENT on the same machine. This might be due to 
different configurations though.

If I run the process with idletime priority, I don't see the problem either.

SCHED_4BSD is not affected.

Hope these findings help fixing the problem.


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