Why is KNLMeansCL slowing me down so much

[Machmir]

But that doesn't explain why that filter was working fine to begin with. And even if my AMD card doesn't work, shouldn't my Intel CPU work in its place?

From https://streamhpc.com/blog/2011-12-29/op...e-support/

AMD/ATI GPUs
Over the years the architecture of AMD/ATI GPUs changed to get better support for OpenCL. Below is a list of GPUs that have good support for OpenCL 1.1 or 1.2.

• Radeon HD 6450 and up.
  

And from CPU-Z it shows SSE4.2 and AVX listed for my CPU