FreeBSD and "make -j# buildworld" usability

[Kent Stewart]

On Monday 16 October 2006 15:33, Garance A Drosehn wrote:
> At 1:47 PM -0700 10/13/06, Kent Stewart wrote:
> >On Friday 13 October 2006 07:31, Buki wrote:
> >>  Hi,
> >>
> >>  I searched the archives and web a little but found many different
> >>  opinions on stability/usability of using make -j# with buildworld
> >>  (and buildkernel).
> >>
> >>  So I am asking if it is a good idea to use make -j on production
> >>  boxes.
> >
> >I tested buildworlds with different values for -j. On single
> > processors, using a script that basically looked like
> >
> >time make -j? ...
> >
> >yielded fastest builds when I didn't specify a value for -j. On dual
> >cpu's a value around -j8 yielded the fastest build.
>
> You might want to repeat those performance tests.  The results will
> change over time, as various system changes are made.  I used to see
> results somewhat similar to yours, but the last time I checked I
> seemed to get the best results from a dual-cpu system when using -j3
> .
>
> I believe that change in performance is due to some improvements
> made to the `make' command itself, which solved some delays that
> happened when -j was used.  However, I do not remember the details.
>
> Performance comparisons like this will also depend on all the
> hardware on the system, and not just the dual-CPU.  It can change
> depending on much memory the machine has, for instance, or how fast
> the disks are compared to the CPU's.

That was why I commented about making your own tests. I had ata-133 or 
100 HDs on individual controllers. Comparing an ata based system with a 
scsi isn't a real comparison.

My tests are at
http://users.owt.com/kstewart/freebsd/urban_legends.html
and I see I got the shortest elapsed time with -j4 and -j8. It has been 
too long to remember what I did to improve the -j8. They were run on 
FreeBSD 4.3 and I no longer have a dual cpu system.

Kent


-- 
Kent Stewart
Richland, WA

http://www.soyandina.com/ "I am Andean project".
http://users.owt.com/kstewart/index.html