Date: Wed, 9 Jul 2003 08:36:53 +1000 (EST) From: Andy Farkas <andyf@speednet.com.au> To: Doug White <dwhite@gumbysoft.com> Cc: freebsd-smp@freebsd.org Subject: Re: whats going on with the scheduler? Message-ID: <20030709080542.H11189-100000@hewey.af.speednet.com.au> In-Reply-To: <20030708113618.P25140@carver.gumbysoft.com>
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On Tue, 8 Jul 2003, Doug White wrote:
> On Tue, 8 Jul 2003, Andy Farkas wrote:
>
> > Any other ideas? Why would 3 (niced) cpu intensive processes suddenly get
> > reduced cpu time (on a 4 cpu system) when a 4th non-resource intensive
> > process gets started?
>
> Hm.. guess its time to explain how nice works again.
>
> Nice is a relative value. If you have 2 processes in a system, one with a
> lower nice value (== higher "priority") than the other, the lower-niced
> process will be scheduled in deference to the higher-niced process. The
> scheduler attempts to ensure that niced processes are not starved. (In
> practice, nice level 20 gets some special treatment.)
That doesn't explain why the idle time goes up, in my case.
If you have 4 processors in a box and start 3 cpu-intensive jobs, the
system load will be 3.00 and idle time will be 25%. If you start another
semi cpu-intensive process, one would expect the load to increase and the
idle time to come down, regardless if the other 3 procs are niced or not.
ps. setiathome procs run at idle level 15.
--
:{ andyf@speednet.com.au
Andy Farkas
System Administrator
Speednet Communications
http://www.speednet.com.au/
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