GPU usage in games

[ManyCowsMoo]

I've been watching my gpu usage in rivatuner while gaming and for certain games, it never reaches 100%. CSS stays at around 30% gpu while cpu usage is 80% for one core and 30% for the other and I play at 1600x1200 max settings 8aa/16af I still get fps dips to 70 or so. Other games aren't as bad, such as Dead Space which stays around 100% gpu and Fallout 3 which stays around 80%. From what I understand, all the parts should work as hard as they can unless they're waiting on input from something else such as the gpu waiting on the cpu. Can anyone enlighten me on this?

 

[BlueStorm]

Not sure what the tool could use as a metric for "GPU utilization" since it's not always very straightforward and I don't think it's exposed, but maybe I'm wrong.

But yes, CPU/GPU can bottleneck each other. If the CPU usage is at 100% you can't feed the GPU any faster, therefore the GPU could easily be a bottleneck in this case. Similarly if GPU is the bottleneck the CPU can't really use all of it's cycles.

 

[Abit667]

GPU utilization is a bit more complicated than just how many fps you're getting or whatever. Even though this is a poor analogy, think of it kind of like how a single threaded application will run on a multicpu system. That application will be performing as well as it can, however there are still a lot of system resources left.

GPUs have a TON of power now, and similar to a multi cpu system, they have a ton of shaders. If the game engine doesn't need any more/can't take advantage of it, it won't be using them and hence your GPU isn't fully utilized. Yet, what is running will speed up and slow down like you'd expect if it were fully loaded.

Obviously older games weren't really designed with that many gpu resources available so they don't take advantage of it. Newer ones that were designed with that level of hardware in mind will though...