This was another dark corner for me. At a high level, it doesn't seem to be too
bad.

I suggest replacing '6.2.9. build/tmp/cache/' with the following:

  When BitBake parses the metadata (recipes and configuration files), it caches
  the results in build/tmp/cache/ to speed up future builds. The results are
  stored on a per-machine basis.
  
  During subsequent builds, BitBake checks each recipe (together with, for
  example, any files included or appended to it) to see if it has been modified.
  Changes can be detected, for example, through mtime changes and hashing of
  file contents. If no changes to the file are detected, then the parsed result
  stored in the cache is reused. If the file has changed, it is reparsed.


Cheers,
Ulf