In setups where only very few elements are processed at once, the lazy-threading
hints that come from `parallel_for` are not triggered. However, often it can
still be worth to use multi-threading in such cases. Therefore, we need to find
additional places where the lazy-threading hints are sent. There are many
possibilities and we probably have to add them step by step as we find .blend
files that show missing multi-threading.
In this patch I choose to send the hint at the beginning of evaluating a repeat
zone if it has 10 or more iterations. The exact number here is just a guess and
could be fine tuned over time if necessary.
A slightly modified version of the file in #134230 speeds up from ~1100ms to
~100ms with this change. The exact speedup changes quite a bit each run, but is
always between 5 and 20x, so it's quite noticable.
Pull Request: https://projects.blender.org/blender/blender/pulls/134408
1cb2d991f9