Compute vs. Fragment shaders

[Josh]

Using a simple passthough shader that just samples a texture and writes to an output image, here are my results.

Framebuffer size is 1280x720
GPU: GEForce 1660
Optimal compute batchsize: 8x8
Optimal compute number of workers: 14400

 

 

1 pass:

Compute
FPS: 600

Fragment
FPS: 770

 

 

10 passes:

Compute
FPS: 180

Fragment
FPS: 670

[Josh]

There may be a way to improve speed of some shaders, but it looks like you are initially battling a really significant drop in performance:

https://forum.beyond3d.com/threads/hardware-gaussian-blur.59951/#post-1972505

[klepto2]

I think your results are correct. The compute shaders are great when you need more complex one time calculations or when you can benefit from cross thread calculations. Eg. Pass the result from one compute batch to another. Also it is very important either fragment or compute to align your memory for your uniforms or buffers in case of vulkan. 
in my experience, while compute shaders can be faster when used for certain scenarios modern fragment features can be better for others. Sometimes it is not only about performance but also about maintability of the code base. And the in my opinion compute shaders are very good, eg terrain editing or particle, agent simulation. 
one should always decide which one fits better to the subject of the shader.