It was caused by image threading safe commit and it was noticeable
only on really multi-core CPU (like dual-socket Xeon stations), was
not visible on core i7 machine.
The reason of slowdown was spinlock around image buffer referencing,
which lead to lots of cores waiting for single core and using image
buffer after it was referenced was not so much longer than doing
reference itself.
The most clear solution here seemed to be introducing Image Pool
which will contain list of loaded and referenced image buffers, so
all threads could skip lock if the pool is used for reading only.
Lock only needed in cases when buffer for requested image user is
missing in the pool. This lock will happen only once per image so
overall amount of locks is much less that it was before.
To operate with pool:
- BKE_image_pool_new() creates new pool
- BKE_image_pool_free() destroys pool and dereferences all image
buffers which were loaded to it
- BKE_image_pool_acquire_ibuf() returns image buffer for given
image and user. Pool could be NULL and in this case fallback to
BKE_image_acquire_ibuf will happen.
This helps to avoid lots to if(poll) checks in image sampling
code.
- BKE_image_pool_release_ibuf releases image buffer. In fact, it
will only do something if pool is NULL, in all other case it'll
equal to DoNothing operation.
Documentation & Test blend files:
------------------
http://wiki.blender.org/index.php/User:MiikaH/GSoC-2012-Smoke-Simulator-Improvements
Credits:
------------------
Miika Hamalainen (MiikaH): Student / Main programmer
Daniel Genrich (Genscher): Mentor / Programmer of merged patches from Smoke2 branch
Google: For Google Summer of Code 2012
a) Another boundary fix. Resulted in smoke getting "sucked" back into the domain
b) Disabling substeps (internal thing). Fixes arbitrary explosions/instabilities.
Part of my Blender Smoke Development.
Detail: Smoke solver and Blender side of smoke now share the same cell length.
First reported by the Sintel artists long ago, again reported by MiikaH.
Part of my Smoke Development Project Phase III.
Sponsored by the Blender Development Fund.
http://www.blender.org/blenderorg/blender-foundation/development-fund/
Remarks:
The original code was not designed to support moving obstacles so I had to introduce some velocity constraints into the code to prevent smoke from exploding. If this causes problems with "fire" emulation, please let me know.
