Hi,
I have tested following with FreeBSD 5.3-Stable.
On several different PCs I have used make -j$n buildworld with $n ranging from 1 to 9.
Although people suggest "-j4" as optimal in general case, I have come to a very different conclusion:
1) single CPU with enough RAM (2 GHz, 512 MB) there's no significant speed up in the range "-j1" to "-j9". So "-j1" is as good as "-j9".
2) single CPU with little RAM (333 MHz, 64 MB) speed slows down rapidly from "-j1" to "-j9", because of intensive swapping. So "-j1" performs best in this case.
3) dual CPU with enough RAM (2 x 800 MHz, 1GB) speed up by almost two from "-j1" to "-j2", but after that no noticeable speed up anymore. So "-j2" is as good as "-j9".
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With these simple tests, I come to the conclusion that "make -j$n buildworld" is best with n = number of CPUs. Does that make sense?
Rob.
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