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Date: Wed, 13 Feb 2008 09:08:42 -0500
From: Bill Moran <wmoran@potentialtech.com>
To: Ed Schouten <ed@fxq.nl>
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Cc: Ian FREISLICH <ianf@clue.co.za>, current@freebsd.org
Subject: Re: Testing box available.
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In response to Ed Schouten <ed@fxq.nl>:

> * Ian FREISLICH <ianf@clue.co.za> wrote:
> > As an aside, a 64 way parallel make buildworld doesn't saturate the CPU.
> 
> I'm not sure, but I think if you do this:
> 
> 	make -j64 <foo>
> 
> it only spawns 64 processes to handle the top level make process. This
> would mean we've got a couple of processes doing this:
> 
> 	make -C bin
> 	make -C lib
> 	make -C sbin
> 	make -C usr.bin
> 	make -C usr.sbin
> 
> and the other processes will just quit, because they don't have anything
> to do. Right? :-)

Basically, -j tells make the _maximum_ number of jobs to run in parallel.
I frequently do -j99, but I've never seen more than about 20.  You can't
just look at it for a second, either.  Certain parts of the build
process have more parallelism available than others, so you might look
at it at a point where there are only a few.

If you really want to saturate it, copy the src tree a few times and
start a make -j99 buildworld in all of them simultaneously :D

-- 
Bill Moran
http://www.potentialtech.com