bitbake: runqueue: Optimise next_buildable_task()

This unlikely looking function was found to be eating a lot of CPU time
since it gets called once per trip through the idle loop if we're not
running a maximum number of processes. This was particularly true in
world builds of 13,000 tasks.

Calling the computation code is pretty pointless because until some
other task finishes nothing is going to become available to build.
We can know when things become available so this patch teaches the
scheduler this knowledge.

It also:

* skips any coputation when nothing can be built
* if there is only one available item to build, ignore the priority map
* precomputes the stamp filenames, rather than doing it every time
* saves the length of the array rather than calculating it each time
  (the extra function overhead is significant)

Timing wise, initially, 5000 iterations through here was 20s, with
the patch 200000 calls takes the same time. The end result is that
builds get up and running faster.

(Bitbake rev: 4841c1d37c503a366f99e3a134dca7440e3a08ea)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions