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List:       fedora-list
Subject:    Re: How to increase maximum user cpu usage allowed on a multi core system?
From:       stan <stanl-fedorauser () vfemail ! net>
Date:       2015-03-17 15:48:57
Message-ID: 20150317084857.14ce5002 () vfemail ! net
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On Mon, 16 Mar 2015 16:05:37 +0100
Heinz Diehl <htd+ml@fritha.org> wrote:

> On 09.03.2015, Martin Cigorraga wrote: 
> 
> > Just a minor clarification: when compiling, the -j flag should
> > point to a unit above your available cores in order to fully
> > utilize all of them.
> 
> Curious what would happen, I remembered this mail when compiling a
> new kernel today. A "nice -n 19 make -j" opened *hundreds* of cc
> incarnations, pushed the load to over 800 and seriously blocked the
> machine (an 8-core Xeon with 16 GB of RAM) within *seconds*!

Lucky you!

Are you using F21?  Which kernel?

So, are you using rpmbuild with the src.rpm package, or compiling
directly from the source tree?

What happens if you use -j 4?  I would think you should get somewhere
between 3 and 4 cores.  The recommendation I saw to fully use all
cores, were from cores+1 to cores*3.  Cores*1.5 was a popular one, to
allow for io slowness.

When I tried -j, I saw all the jobs queue, but only one core was used.

Thanks for reporting back.
-- 
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