CPU usage calculation in time profiler instrument

Question

When I use time profiler in instrument, it shows the cpu usage for each core (or logical core) as well as a "cpu usage". I'm wondering how the cpu usage is calculated according to the cpu usage of each core. I tried data from a specific timestamp and it is neither sum of each core nor average. Here is a snapshot of the panel.

Answer 1

The CPU usage is neither the sum nor the average. In contrast to OS CPU usage (say top), profile CPU usage is generally taken from an actual hardware counter in the processor. This also makes it hardware dependent, meaning its exact meaning on an Intel processor is different from that of an AMD processor. So why are these measurements useful? Because the ratios and values are correct when compared to values taken over the same interval / at the same instant, and the average values are what you expect them to be.

When profiling, look at correlations first over intervals and then between intervals. Afterwards, zoom in on more specific registers, such as cache misses or pipeline stalls.

You might check out the Intel optimization documentation. It's pretty good in my experience. I'll post a reference in the comment section if I can find the time.

PS By the way, the "Core 4" and "Core 5 (logical)" are really not accurate above (not your fault). The names imply that the "logical" core is somehow inferior to the non-logical one. When a CPU is executing multiple hardware threads on one core, what Intel in marketing speak calls hyperthreading, there is no difference between Core 4 and Core 5 as they behave identically on the physical core -- meaning they are both "logical".