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Date: Mon, 29 Oct 2012 20:33:44 -0500 (CDT)
From: Steven Nikkel <steven_nikkel@ertyu.org>
To: freebsd-stable@freebsd.org
Subject: CPU Competition Issue
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I'm running a long duration CPU-centric process that will gobble up all 
available CPU time. I have it set to run at nice +20. While it's running 
I've noticed other processes have a hard time getting CPU time and run 
their activites very slowly. The processes I've noticed issues with are IO 
involved, but they don't appear to be IO blocked as they run dramatically 
faster and use much more CPU time when the CPU intensive process is 
not running. I haven't noticed issues with other processes, but I haven't 
been looking. If I push my CPU intensive process into idle priority 1, all 
the other processes return to their normal behaviour as if it's not 
running.

This seems to be a specific behaviour on this one machine 
running 9.0-RELEASE-p4 on an Atom 330 dual core. I've tried with and 
without hyperthreading enabled with no noticeable change in behaviour.