BLI_task: tweak default chunk size for `BLI_task_parallel_range()`.

Previously we were setting it to 1 (aka no 'chunking'), to follow
previous behavior. However, this is far from optimal, especially with
CPUs that can have tens of threads nowadays.

Now taking an heuristic approach (inspired from the one already existing
for `BLI_task_parallel_listbase()`, which tries to guesstimate best
chunk sizes based on several factors (amount of threads/parallel tasks,
total number of items, ...).

Think this is a reasonable base ground, more optimization here would of
course be possible.

Note that code that was already explicitely settings some value here
won't be affected at all by that change.

1 files changed, 2 insertions, 5 deletions

diff --git a/source/blender/blenlib/BLI_task.h b/source/blender/blenlib/BLI_task.h
index d11ba15a7e0..85680d8aae8 100644
--- a/source/blender/blenlib/BLI_task.h
+++ b/source/blender/blenlib/BLI_task.h
@@ -216,11 +216,8 @@ BLI_INLINE void BLI_parallel_range_settings_defaults(ParallelRangeSettings *sett
   memset(settings, 0, sizeof(*settings));
   settings->use_threading = true;
   settings->scheduling_mode = TASK_SCHEDULING_STATIC;
-  /* NOTE: Current value mimics old behavior, but it's not ideal by any
-   * means. Would be cool to find a common value which will work good enough
-   * for both static and dynamic scheduling.
-   */
-  settings->min_iter_per_thread = 1;
+  /* Use default heuristic to define actual chunk size. */
+  settings->min_iter_per_thread = 0;
 }
 
 #ifdef __cplusplus