Build Optimizations

Here are some optimizations to increase build time.  These create source and sstate cache mirrors that can be used by multiple users on a build host.

Setting up a source file mirror

1. Setup a workspace based on the branch to mirror (e.g. kirkstone, rdkb-2024q1-kirkstone, rdkb-2024q2-kirkstone).
2. Add this to conf/local.conf to generate tarballs of git repos downloaded during the fetch process.
   1. BB_GENERATE_MIRROR_TARBALLS = "1"
3. Run the fetch task for the image
   1. bitbake target --runonly=fetch
4. When bitbake completes, the download directory will contain tarballs of source files used during the build. Copy the files to the download mirror directory.  Use --dry-run to see if everything looks sane.  Example command to copy the files.
   1. rsync --exclude=*.done --dirs -v --info=nonreg0 downloads/ /srv/rdkmirrors/downloads
5. Add these to conf/local.conf to use the source mirror
   1. SOURCE_MIRROR_URL ?= "file:///srv/rdkmirrors/downloads"
   2. INHERIT += "own-mirrors"

References

• https://docs.yoctoproject.org/4.0.20/singleindex.html#replicating-a-build-offline
• https://docs.yoctoproject.org/bitbake/2.0/singleindex.html#term-BB_GENERATE_MIRROR_TARBALLS
• https://www.thegoodpenguin.co.uk/blog/improving-yocto-build-time/

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