If the processor is constantly pegged at 100%, but the graphics card is hovering under 90% usage, then you have a CPU bottleneck. On the other hand, if your GPU is constantly at 100% and the CPU is under 90%, then it's a GPU bottleneck.

Does CPU really bottleneck GPU?

If the CPU load is very high (about 70 percent or more) and significantly higher than the video card's load, then the CPU is causing a bottleneck.

Is GPU bottleneck better than CPU bottleneck?

Basically, the CPU sets the max framerate, based on the game. The GPU sets the max framerate, based on the game, and the resolution. And as long as your max framerate is above the refresh rate of the monitor you're using, on the games you're playing, a bottleneck really doesn't matter much.