[Bf-cycles] Tiles sizes - impact on RAM and speed

[Ole Jakob Skjelten]

Andrew Price posted some results (http://www.blenderguru.com/4-easy-ways-to-speed-up-cycles/) and with the sweet spot being at 256x256 for GPU and 16x16 for CPU. But like Brecht said, it gets more complicated. Let's say that your full resolution render is a multiple of 128 but not of 256. In that case you end up wasting time as cycles finishes the half tiles you "missed" using 256x256 versus using 128x128. 

So I guess any benchmark will only be relevant for the resolution the benchmark is using, so my quest for the "one rule to rule them all" isn't quite as straightforward as I'd liked ;)

OJ 

--
Ole Jakob Skjelten
olesk at pvv.org
+41 79 832 2976




On 10. feb. 2013, at 19:00, Constantin Rahn <crahn at vrchannel.de> wrote:

> The magic number for fastest GPU rendering seems to be >= 128x128
> 
> I have posted some values in the benchmark thread on BA:
> http://blenderartists.org/forum/showthread.php?239480-2-61-Cycles-render-benchmark&p=2287569&viewfull=1#post2287569
> On a GTX580 128x128 is two times faster than with 64x64.
> 
> Am 10.02.2013 18:45, schrieb Brecht Van Lommel:
>> On Sun, Feb 10, 2013 at 5:52 PM, Ole Jakob Skjelten <olesk at pvv.org> wrote:
>>> Thanks a lot for that Brecht! My understanding is that *reducing* tile sizes
>>> only has a positive effect with regards to reducing the size of the output
>>> buffer, which is in most cases is a rather small part of the total RAM eaten
>>> by Cycles, and thus, unless you you're in a desperate
>>> I-only-need-10MB-more-RAM-to-render-on-my-GPU scenario, increasing the tile
>>> size for speed benefits is the more likely scenario. Would you agree?
>> Yes, I agree. Maybe if you have a ton of render passes, but otherwise
>> you can quite safely set it quite large.
>> 
>>> It's also my understanding that, using CUDA, keeping your tiles to multiples
>>> of 16 pixels helps speed (or rather prevent wasting GPU cycles)? And
>>> finally, does it help to operate with tiles that are multiples of the full
>>> render resolution, or should one use same values for x and y direction
>>> (square tiles) instead?
>> Multiples of 16 might indeed help, I'm not quite sure if this true in
>> general though and if this perhaps depends on the particular GPU.
>> Multiples of the render resolution will help if you use big tiles,
>> since otherwise you can get some smaller tiles to fill up the full
>> render.
>> 
>> Brecht.
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> 
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