Deferred rendering is working nicely now.  I even sped up the ray marching compute shader by changing local_size_x from 1024 to 64.  I've got mipmaps and voxel level ambient occlusion optimization bits working again.  The ray marching compute shader is only run when something changes in the world and/or the camera location or direction changes.  I'm seeing some very high frame rates (3000+) when the game is just rendering from the gbuffer and not running compute shaders (raymarch, mipmaps update, voxel ao bits update).  In this scene, when the camera position changes with free look, raymarch takes between 0.0040 and 0.0050 seconds to run and the frame rate drops to between 130 and 200.  I'm still not sure why the framerate drops so low when the ray marching compute shader is running.

(Fragment shading rates aren't currently working because that needs to be implemented in the raymarching compute shader.)