Make buildworld

Josh Carroll josh.carroll at gmail.com
Mon Jun 9 05:35:04 UTC 2008


> I did some testing, at least for me, I get the most improvements when the number
> of cores or processors equals the -j number.  You can make it higher, even
> double it, withoout hurting things, but 95% of the improvements come from
> matching the number of processes to the number of available CPUs (and that' by
> my own testing, not theory).

I've found that on my Q6600 (quad core) system, the optimal is 8
though the improvements after 5 were minimal. It depends if the jobs
are I/O bound or not and the scheduler. Although even with ffmpeg, the
optimal number of threads with this quad core system is 8. On my
previous system with a dual-core chip with the same hardware, the
"magic number" was 4 (again, 2x the number of cores). This was with
the ULE scheduler, I'm not sure if the same holds true for the 4BSD
scheduler or not.

And as you said, it's important to use make without -j if the build
fails before reporting bugs, since there are no guarantees that world
will build properly with multiple jobs.

Josh


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