Use all the cores or CPUs when compiling

make -j 4
Force make command to create as many compile processes as specified (4 in the example), so that each one goes into one core or CPU and compilation happens in parallel. This reduces the time required to compile a program by up to a half in the case of CPUs with 2 cores, one fourth in the case of quad cores... and so on.

16
By: kovan
2009-08-05 22:50:57

What Others Think

Is there an easy way to know how many CPUs you have? Then the command could be: make -j $(cat /proc/cpus)
matthewbauer · 528 weeks and 1 day ago
Your compilation only experience a n-fold linear speedup (with n being the number of CPU/cores) if your code has only parallel components and no serial components (dependencies in your code). In the case of even a slight amount of serial components (i.e. 1-2%), speedup is greatly affected. This is the essence of Amdahl's Law.
DeusExMachina · 528 weeks and 1 day ago
@mattthewbauer in Linux you could do somethink like make -j $(grep -c ^processor /proc/cpuinfo). It doesn't do any bad to use a higher number than the actual number of cores thought. @DeusExMachina: true but usually the speed increase is linear or nearly linear, because AFAIK in Makefiles interdependencies only exist between targets, so all the source files of each target can be compiled in parallel.
kovan · 528 weeks and 1 day ago
From my make manpage, "If the -j option is given without an argument, make will not limit the number of jobs that can run simultaneously." That suggests this command shouldn't help at all. Am I wrong?
tremby · 525 weeks and 4 days ago
Oh, facepalm. I read it (more than once) as "If the -j option is not given". Never mind.
tremby · 525 weeks and 4 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

You must be signed in to comment.

What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

Share Your Commands



Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for: