Date: Tue, 23 Nov 2004 14:08:16 +0900 From: Rob <spamrefuse@yahoo.com> To: freebsd-stable@freebsd.org Subject: make -j$n buildworld : use of -j investigated Message-ID: <41A2C5C0.3080908@yahoo.com>
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Hi,
I have tested following with FreeBSD 5.3-Stable.
On several different PCs I have used
make -j$n buildworld
with $n ranging from 1 to 9.
Although people suggest "-j4" as optimal in general
case, I have come to a very different conclusion:
1) single CPU with enough RAM (2 GHz, 512 MB)
there's no significant speed up in the range
"-j1" to "-j9".
So "-j1" is as good as "-j9".
2) single CPU with little RAM (333 MHz, 64 MB)
speed slows down rapidly from "-j1" to "-j9",
because of intensive swapping.
So "-j1" performs best in this case.
3) dual CPU with enough RAM (2 x 800 MHz, 1GB)
speed up by almost two from "-j1" to "-j2",
but after that no noticeable speed up anymore.
So "-j2" is as good as "-j9".
----------------------------------------
With these simple tests, I come to the conclusion that
"make -j$n buildworld" is best with n = number of CPUs.
Does that make sense?
Rob.
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