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I have a Makefile on a machine that has a ton of cores in it, but I always seem to forget to write -jX when compiling my project and it takes way longer than it should.
Is there some way I can set the -j flag through an environment variable or some other persistent config file so that make will automatically execute multiple jobs in parallel on this machine?
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The -j flag tells the make command simultaneously to run independent targets. If you follow the -j option with an integer, then the integer specifies the maximum number of concurrent jobs that can be executed to build the targets.
Currently when passing "-flto" for enabling Link-Time Optimizations with the GCC compiler, it defaults to using a single core/thread for carrying out the optimizations and code generation.
I'm assuming you're using Linux. This is from my ~/.bashrc
# parallel make export NUMCPUS=`grep -c '^processor' /proc/cpuinfo` alias pmake='time nice make -j$NUMCPUS --load-average=$NUMCPUS' sample usage
samm@host src> echo $NUMCPUS 8 samm@host src> pmake becomes time nice make -j8 --load-average=8.
To answer your specific question about putting this into a Makefile, I don't find it practical to sprinkle this logic all over my Makefiles. Putting this into a top level Makefile also isn't a great solution since I often build from sub-directories and wish to build them in parallel as well. However, if you have a fairly flat source hierarchy, it may work for you.
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