Originally Posted by Arni90
While it certainly is nice to monitor CPU usage, it's ultimately useless to determine bottlenecks as windows likes to assign processor load across several cores and Amdahl's Law and Hyperthreading makes things even more complicated. Short story, CPU usage is useless to determine processor bottlenecks unless you're running a single core without hyperthreading.
GPU Usage, on the other hand, is a lot more informative as a non-99% usage indicates a PCIe/CPU-bottleneck (which with todays CPUs means the same thing: swap processor for better performance.)
1000x THIS. Man I wish I didn't have to explain this over and over to people on these boards
However, the TOTAL cpu usage % can be somewhat useful if you know for certain how many cores a game is coded for. I.E. if you have 4 cores, and you know the game is coded for only 2, and you see usage pegged at 50% total on a quad-core ... it's pretty well indicative that there could be CPU BN going on. However the converse is not necessarily true ... can't rule out a CPU BN just cause you're not at 50%, IOW.
Also I should point out there's other bottlenecks that can cause <99% usage aside from CPU/PCIe. Could also be a lack of system RAM, for example. Additionally, the BN can even be internal to the card itself, such as by over-saturation of memory subsystem bandwidth, or vram capacity being tapped out, in the particular gaming scenario at hand. And driver or game bugs can also cause it ... through various mechanisms like causing excessive texture swapping or causing a lot of cache misses to occur