My old setup: AMD Phenom II X6 1055T at 2400 MHz, 32 GiB DDR3 RAM at 1200 MHz, (1600MHz when SPD works), nVidia GTX 760. Nothing overclocked. GPU render was about 3× faster than CPU (with or without Open Shading Language, which did not always work). Nothing over clocked. The GPU is a PCIe 3.0, but the MB is a PCIe 2.0.
New setup: AMD Ryzen 7 3800X, 32 GiB DDR4 RAM at 3200 MHz (with SPD, normally 2400), same GPU, but now in a PCIe 4.0 MB. Nothing overclocked. (Yes, I replaced my ten year old MB and CPU, thus had to also get new RAM). All else equal. —OS on SATA III SSD, data on 4× HDD RAID5, SATA III, OS (Ubuntu 20.04 LTS) et al. No surprise, CPU render is now faster than GPU render. In fact, it is about 3× faster. What I found surprising is that GPU+CPU render is slower than plain old CPU, and plain old CPU is faster than CPU with OSL. I thought that a car being pushed by four strong guys will go slower than a car being pushed by four strong guys and one weakling, thus, adding the slower GPU would still speed up the render. Apparently not. I also recall on my old system, that GPU+CPU was also slower than just plain GPU. In other words, the slower guy slows down the faster guy, either way. I do not think it was supposed to work that way. Second, I thought that OSL accelerated surface/volume scattering when doing physics-based rendering, (my normal MO). I cannot ever remember actually timing it on the old system, but I do remember getting the perception of it taking longer whenever OSL crashed Blender. Very non-scientific. Does using OSL slow us down as a trade-off for better render. or does it accelerate the system?. Should GPU+CPU be faster than just one or the other? Old system was Blender 2.90.1, compiled from source. New system is Blender 2.91.0, also compiled from source. (I also re-compiled some of the dependencies after the upgrade to ensure any new available compile options are used to optimize for the new platform). Sincerely, Karim Hosein Top Rock Photography 754.999.1652 ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
