Jeff Lait

Thank you for testing! Glad this was the source of the problem. IIRC, the fix to our interop woes was not trivial to backport, which is why we chose just to leave it disabled in the current version.

It was just pointed out to me that we have interop disabled in H21 because of some driver leaks we weren't able to address in time. Living in the future, as I am, I already had the fast interop.

You can try forcing interop to run anyways with:
HOUDINI_COP_RASTERIZE_INTEROP
You have to set this environment variable to 1 and see if it unlocks faster speed. It probably will cause a VRAM leak that will result in unhappiness, however. But it would be good to know if it makes it fast so we know that when this is fixed in future versions you will get a faster rasterize....

To make sure we are on the same page, does the attached show the disparity for you? Or please provide a .hip that shows the disparity.

I currently know of two possible failure modes. If we fall back to software vulkan, it definitely is game over. But we can also have the vulkan device and OpenCL device not be on same system, which disables interop.