I’m trying to determine if this is a bug I should report, or if this is a known limitation of GPU subdivision: when I move the shapekey sliders on a subdivided mesh the performance was extremely poor on my new computer, which was odd because it’s much more powerful than my old computer. On a whim, I tried disabling GPU subdivision since it’s a new feature, and the problem was fixed, instantly. Subdivision is the only modifier on the stack, so it’s not issue with the modifier order. Not sure if my previous computer had GPU subdivision in use in Blender.
I know that GPU subdivision is supposed to be more efficient, but while modifying shapekeys at least, it was sluggish to the point of basically freezing for a second or two. Is that the expected behavior, or is there a bug? Or maybe a hardware compatibility issue, but my new graphics card is vastly superior to my old one, 3D navigation is smooth in heavier scenes.
Your observation was discussed and opened in this issue report a few months ago. Most people weren’t able to reproduce this performance issue however.
Is your GPU integrated chance? If your GPU is integrated, it’s possible your CPU is stronger then your GPU in terms of speed and cannot take fully take advantage of the GPU computing that Blender has for GPU Subdivision.
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I have a dedicated NVIDIA GeForce RTX 3080 Ti as well as an integrated Intel whatever GPU, but I’ve set Blender to the NVIDIA card. That’s a fairly powerful card to my knowledge, so I wouldn’t think you’d need much better, but there could be some other driver issue or compatibility problem I suppose.
Either way, you have answered the question. Looks like it’s a known issue, even if the exact cause isn’t known. I can live without the GPU subdivision, so it’s enough to know this isn’t the expected behavior, and the devs are aware of the problem. Thanks!