by Lewis » Fri Jun 03, 2022 12:26 pm
Lewis
Fri Jun 03, 2022 12:26 pm
Another thing what could it be is OutOfCore RAM usage, since your PC GPU is connected to monitors it has less free VRAM (windows and just on monitor eats about 350-400 MB and more resolution/monitors and layout OGL itself it can easily go to 2 GB Vram usage which is not then available for Octane and then the more OCC render uses the slower render it gets.
Margin of slowdown with increased OCC is very, very big.
I tested this few years ago and after 30-40% of OCC render can slow down like 5x or more...
So in your case those GPUs in external have more FREE VRAM, so it uses less OCC, and thus it can almost be faster than using all 3 GPUs since then OCC is bottlenecking all GPUs.
check my results with OCC:
Test 1 (4*2080 Ti) - Denoiser ON, Parallel samples=16, Max Tile samples=32
_____________________
GPU headroom = 300 MB
Out of Core = 0 MB
Rendertime = 1m 8sec (68sec)
Test 2 (4*2080 Ti) - Denoiser ON, Parallel samples=32, Max Tile samples=64
_____________________
GPU headroom = 300 MB
Out of Core = 768 MB
Rendertime = 1m 18sec (78sec) = 15% slower
Test 3 (4*2080 Ti) - Denoiser ON, Parallel samples=32, Max Tile samples=64
_____________________
GPU headroom = 512 MB
Out of Core = 1024 MB
Rendertime = 1m 32sec (92sec) = 35% slower
Test 4 (4*2080 Ti) - Denoiser ON, Parallel samples=32, Max Tile samples=64
_____________________
GPU headroom = 1024 MB
Out of Core = 1792 MB
Rendertime = 2m 04sec (124 sec) = 82% slower
Test 5 (4*2080 Ti) - Denoiser ON, Parallel samples=32, Max Tile samples=64
_____________________
GPU headroom = 2048 MB
Out of Core = 2816 MB
Rendertime = 2m 57sec (177 sec) = 160% slower
Test 6 (4*2080 Ti) - Denoiser ON, Parallel samples=32, Max Tile samples=64
_____________________
GPU headroom = 4096 MB
Out of Core = 4989 MB
Rendertime = 16m 03sec (963 sec) = 1315% slower
--
Lewis
http://www.ram-studio.hrSkype - lewis3d
ICQ - 7128177
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