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ARC cycles oneAPI rendering without ReBAR

yo, big shout out to the Cycles team for getting the oneAPI backend working seamlessly.

i bought an ARC A770 16GB as a gamble, because my computer does not support resizable BAR (ReBAR). my thought process was that since Cycles uploads everything at the start of the process to the card and then spends most of its time rendering, the performance hit would be OK.

after testing i can say, cycles does work perfectly as a render device even without ReBAR. very unscientific benchmarks place it somewhere around 2x as fast as a GTX 1080, comparing CUDA to oneAPI (OPTIX is cheating because the BVH generation is much faster and happens on the GPU). this is a bit slower than opendata suggests (opendata score is 2x 1080 TI) but is more than enough for me for the $350ish i paid for it.

other parts of blender are hit and miss without ReBAR. viewport navigation is tolerable but lookdev/Eevee are slideshows. hilariously, cycles viewport (1-2 FPS) is faster than Eevee viewport (1-2 seconds per frame). the cycles perf can only go up when open image denoise gets GPU acceleration. also, if you put a RTX card in the system, even without connecting a display (i.e., you’re using the ARC as primary display), blender will automatically use it as an optix device for the optix denoiser without any issues!

doing a UEFI patch to force ReBAR to 1GB (don’t do this, it’s buggy AF at least on my old haswell board) make Eevee usable. i can’t wait to try it on a newer computer with full ReBAR support. but i’ll probably put this card in a linux server (when drivers are more stable) and use it as a headless render device.

i’m looking forward to seeing the rt hardware for oneAPI in blender 3.5

if you need a benchmark on old hardware, let me know. i have it in spades.

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