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@@ -347,6 +347,53 @@ Refer to the help text of this script for more details:
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utils/size-stats-compare -h
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----------------
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+[[top-level-parallel-build]]
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+=== Top-level parallel build
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+
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+.Note
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+This section deals with a very experimental feature, which is known to
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+break even in some non-unusual situations. Use at your own risk.
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+
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+Buildroot has always been capable of using parallel build on a per
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+package basis: each package is built by Buildroot using +make -jN+ (or
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+the equivalent invocation for non-make-based build systems). The level
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+of parallelism is by default number of CPUs + 1, but it can be
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+adjusted using the +BR2_JLEVEL+ configuration option.
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+
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+Until 2020.02, Buildroot was however building packages in a serial
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+fashion: each package was built one after the other, without
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+parallelization of the build between packages. As of 2020.02,
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+Buildroot has experimental support for *top-level parallel build*,
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+which allows some signicant build time savings by building packages
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+that have no dependency relationship in parallel. This feature is
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+however marked as experimental and is known not to work in some cases.
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+
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+In order to use top-level parallel build, one must:
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+
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+. Enable the option +BR2_PER_PACKAGE_DIRECTORIES+ in the Buildroot
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+configuration
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+
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+. Use +make -jN+ when starting the Buildroot build
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+
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+Internally, the +BR2_PER_PACKAGE_DIRECTORIES+ will enable a mechanism
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+called *per-package directories*, which will have the following
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+effects:
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+
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+* Instead of a global _target_ directory and a global _host_ directory
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+ common to all packages, per-package _target_ and _host_ directories
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+ will be used, in +$(O)/per-package/<pkg>/target/+ and
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+ +$(O)/per-package/<pkg>/host/+ respectively. Those folders will be
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+ populated from the corresponding folders of the package dependencies
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+ at the beginning of +<pkg>+ build. The compiler and all other tools
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+ will therefore only be able to see and access files installed by
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+ dependencies explicitly listed by +<pkg>+.
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+
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+* At the end of the build, the global _target_ and _host_ directories
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+ will be populated, located in +$(O)/target+ and +$(O)/host+
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+ respectively. This means that during the build, those folders will
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+ be empty and it's only at the very end of the build that they will
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+ be populated.
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+
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include::eclipse-integration.txt[]
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include::advanced.txt[]
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