Vulkan: Tuning warptile for Mali GPU Performance

[rmatif]

I'm working on Local Diffusion, using stable-diffusion.cpp on Android. Vulkan performance on Mali GPUs is currently very poor

Disabling mul_mat_l in ggml-vulkan.cpp helped a bit. I then tried modifying the m_warptile and s_warptile values. Reducing the first element (m tile?) from 128 to 64 gave a ~3x inference speedup, but the output images were garbage/noisy.

Questions:

• How can I correctly tune m_warptile and s_warptile for Mali GPUs to get both performance and correct output?
• Are there specific alignment requirements for these values on Mali?
• Do the matmul shaders need to be adapted if these warptile values are changed?

Looking for guidance to improve Vulkan matmul performance on Mali without breaking correctness