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There are two independent dimensions of parallelization:
The maximum number of packages processed in parallel when using the parallel executor. This dimension can be limited with the option --parallel-workers NUMBER. It can also be limited to 1 by selecting the sequential executor with --executor sequential.
The maximum number of threads used for a specific package using make. This can be controlled using the environment variable MAKEFLAGS. By setting e.g. export MAKEFLAGS="-j 4" only four threads are used to build a single package. By default colcon-cmake uses the number of available CPU cores (including hyper threading) to limit the number of threads (-j) as well as the system load (-l).
As a result the overall number of threads is the product of packages processed in parallel and maximum number of threads per package.
For anyone finding this, I found that colcon build on a Raspberry Pi 4 can crash, but adding --executor sequential sorted this out without a massive time penalty.
--parallel-workers NUMBER is the syntax you're looking for. "-j N" is a make specific argument.
There's documentation of the parallel executor command line options here: https://colcon.readthedocs.io/en/rele...
Asked: 2020-12-22 12:15:44 -0500
Seen: 11,887 times
Last updated: Dec 31 '20
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