Games absolutely yield, even if the rendering thread tries to go 100% you'll likely still be sleeping in the GPU driver as it waits for back buffers to free up.

Games absolutely yield, even if the rendering thread tries to go 100% you'll likely still be sleeping in the GPU driver as it waits for back buffers to free up. Even for non-rendering systems those still usually run at game tick-rates since running those full-tilt can starve adjacent cores depending on false sharing, cache misses, bus bandwidth limits and the like. I can't think of a single title I worked on that did what you describe, embedded stuff for sure but that's a whole different class that is likely not even running a kernel.