Parallel builds under yocto

["Monsees, Steven C (US)" <steven.monsees@baesystems.us>]

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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.

BB_NUMBER_THREADS defines number of threads dedicated for bitbake.

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 ?

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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