how to: make -j x // where x is automatically determined

Question

After reading answer to this question: Make "make" default to "make -j 8"

I am wondering if there is way to make the -j option automatically use the correct number of compile threads?

So I say make. And the make command itself uses 6 or 4 or 8 threads depending on the hardware?

@maba usually the recommendation is to use the number of cpu cores x 2. So for a a dual core cpu, it should be -j 4. But some recommend as many compile threads as cores. So -j 2 for a dual core cpu. — Ahmad Mushtaq, Jun 08 '12 at 09:43

score 15 · Accepted Answer · edited May 23 '17 at 11:46

15

make does not look up the number of cores by itself if you just use make -j -- instead, it parallelizes to the max. However, you should be able to determine the number of cores by

grep -c "^processor" /proc/cpuinfo

or (as per Azor-Ahai's comment, if available on your system)

nproc

Hence:

make -j $(nproc)

See "How How to obtain the number of CPUs/cores in Linux from the command line?" for more details. Also, see GNU make: should the number of jobs equal the number of CPU cores in a system?

edited May 23 '17 at 11:46

Community

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answered Jun 08 '12 at 08:28

krlmlr

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I think that this isn't the answer that the user want .... But the question isn't very clear... – DonCallisto Jun 08 '12 at 08:31
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@DonCallisto: No, the question is perfectly clear to me: Use `-j 17` if there are 17 cores. I just remembered the semantics of `-j` wrong. – krlmlr Jun 08 '12 at 08:33
now your answer have much sense ... remember to add the section where you create the alias ;-) – DonCallisto Jun 08 '12 at 08:39
@DonCallisto: This has been treated in the referred-to question already. – krlmlr Jun 08 '12 at 08:50
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Is this any different than using `nproc`? – Azor Ahai -him- May 11 '16 at 17:15
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@Azor-Ahai: I don't think so, thanks for showing me `nproc`! – krlmlr May 11 '16 at 17:19
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One should use `nproc` instead of `cpuinfo` or `lscpu` because `nproc` correctly handles offline cores and CPU affinity. Trying to scale to cores that are not in use is bad. – Mikko Rantalainen Aug 16 '22 at 19:36

how to: make -j x // where x is automatically determined

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