Also there are sensible defaults for both, which use autodetection for how many cores a system cpu has. Generally you need to start tweaking these settings only when defaults aren't working well (e.g. if the system doesn't have enough RAM to support that many instances of gcc).
Alex On Wed, 14 Aug 2024 at 21:25, Khem Raj via lists.yoctoproject.org <raj.khem=gmail....@lists.yoctoproject.org> wrote: > > On Wed, Aug 14, 2024 at 12:15 PM Monsees, Steven C (US) via > lists.yoctoproject.org > <steven.monsees=baesystems...@lists.yoctoproject.org> wrote: > > > > Hello: > > > > I am looking for some clarity with regards too parallel builds under Yocto… > > > > I think I had a false assumption on setting PARALEL_MAKE… > > > > To increase thread usage: You add following to your local.conf inside the > > build/conf directory. Replace x and y with your wanted configuration. > > > > PARALLEL_MAKE = "-j x" > > > > > > > > BB_NUMBER_THREADS = "y" > > > > > > > > Is the following true ? > > > > > > > > PARALLEL_MAKE defines how many threads should be used/dedicated when using > > make -j command during do_compile. > > > > > > seems correct. > > > > > BB_NUMBER_THREADS defines number of threads dedicated for bitbake. > > It means how many jobs/tasks can bitbake spawn in parallel, its higher > order than parallel make. > > > > > > > > > I set up like so: > > > > > > > > There are 12 cores my board > > > > > > > > Yocto supporters say threads should be 2 times the number of cores, but > > don’t go above 20…, or just the number cores, also under 20… depending on > > what you read. > > > > > > > > They also say, increasing PARALLEL_MAKE to higher values, increases your > > chance for a race condition. > > > > > > > > Is the following true ? > > > > > > > > PARALLEL_MAKE = "-j x" # For do_compile > > > > > > > > BB_NUMBER_THREADS = "y" # For bitbake > > > > > > > > PARALLEL_MAKEINST = "-j x" # For do_install > > > > > > > > If so, does this mean for 12 cores: > > > > > > > > BB_NUMBER_THREADS="8", will this dedicate 8 cores just for bitbake to use ? > > No, it will not reserve 8 cores, rather it tells bitbake to launch 8 > task executions in parallel > if bitbake deems them not dependent upon each other, e.g. every recipe > has several tasks > during build do_confgure, do_compile, do_install etc. and there are > several recipes in build > queue, then bitbake's task manager can find out non-dependent tasks > and execute them > in parallel, now be aware that in some cases it could be executing 8 > tasks which could be > all do_compile tasks for different recipes, in this case your > parallelism will become -j 8*8 > systemwide. > > > > > > > > > And does this dedicate the remaining 4 for do_compile and do_install ? > > > > > > > > PARALLEL_MAKE="-j 2" > > > > PARALLEL_MAKEINST="-j 2” > > > > > > > > Thank you… > > > > > > > > Steve > > > > > > > > > > > > > > >
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