Rob wrote:
Brian Szymanski wrote:
Did you try any machines that used Hyperthreading? I'd be interested to
see how those machines fare based on the number of logical and real CPUs.
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".
If you went to all that trouble, you might as well post the numbers :-)
Time unit is minutes.
CPU: 2x800 MHz 2000 MHz 333 MHz
RAM: 1024 MB 512 MB 64 MB
-j --------------------------------
1 99 50 276
2 58 49 291
3 58 50 367
4 57 50 547
5 58 49
6 58 50
7 57 50
8 58 50
9 58 50
I have run another test on a 700 MHz, 128 MB PC,
and the following equation seems to hold for all
my tests. Calculate:
time(minutes) * speed(MHz) * nproc / 1000 MHz
and if this results in approximately 1, the system
is optimized.
For example, in the above case,
column 1:
-j1 : 99 * 800 * 2 / 1000 = 1.5
-j2 : 58 * 800 * 2 / 1000 = 0.928
column 2:
-j1 : 50 * 2000 * 1 / 1000 = 1
column 3:
-j1 : 276 * 333 * 1 / 1000 = 0.919
another PC:
-j1 : 142 * 700 * 1 / 1000 = 0.994
--------------
All PCs have "standard" hardware. Off-the-shelf
mainboard, IDE harddisks, nothing special really.
All this is done on 5.3-Stable systems and the time
listed (in minutes) is for the buildworld only:
"make -jn buildworld"
Rob.
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