by dpJudas » Sat Feb 11, 2017 5:30 pm
What graphics card do you use and at which resolution do you play at? Note that the AO in particular is quite expensive on the GPU side of things, especially if you put its quality setting at max and use a high multisampling setting. Cranking up the AO portal slider can be a true killer on a map where you can see a lot of portals.
About the CPU and GPU usages, what is going on here is that the main GZDoom rendering is CPU bound. That means the GPU is bored and waiting for the CPU to feed it more walls and floors. The AO on the other hand is very much GPU bound, but it only runs after the entire scene has been rendered. So you get the worst of both worlds here - first the GPU is bored waiting for the CPU, and then afterwards the GPU is very busy AO'ing while the CPU is bored.
One last thing about CPU usage percentages: most applications only use one core for various reasons (in GZDoom's case it is because access to the OpenGL context needs to happen on one thread). If you have 4 cores, then a value near 25% CPU usage means that a single core is maxed out. Even if you take something like QZDoom's multithreaded software renderer, you'll typically never see 100% CPU usage because about 30% of the time the other cores are bored waiting for the main render thread to feed them with stuff to do.