about parallelized building

Jean-Baptiste Faure jbf.faure at sud-ouest.org
Wed Nov 7 02:18:06 PST 2012


I noticed that options --with-max-jobs= and --with-num-cpus= are not
recognized anymore. Instead of that we have only --with-parallelism or
My question is : does that mean that it is not possible to use
parallelism but with only a part of the available cpus?

My problem is that I build LO on my laptop and full parallelism has
several drawbacks for me:

1/ the laptop reaches the alarm threshold for the temperature so I need
to downgrade the CPU frequency

2/ the laptop is not very responsive if I want do something else during
LO building. I had not this problem when I could use --with-max-jobs=2
and --with-num-cpus=2

3/ my laptop has an i7 and Linux (Ubuntu 12.04 x86_64) sees 4 cpus when
there is only 2 physical cpus, because i7 uses hyperthreading to
simulate 2 cpus on each physical core.
In my day job I write parallelized computer codes using OpenMP in
Fortran 2008, and I saw that using 4 cpus, 2 being virtual, is less
efficient than using 2 real cpus on i7 processors. I can't say that it
is the same when building LO, but perhaps.

So I think it should be useful if we could set the number of cpu to use
for building LO.

Best regards.

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