How CPU speed is managed vs CPU utilization

cpu usageintel-core-i7performance-monitor

I often see, in the performance monitor, CPU speed varying according to CPU utilization: When utilization increases speed increases:

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However sometimes this relationship is inverted: Speed increases when utilization decreases:

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On the image above, most of the time CPU is decreased for load peaks, but the direct relationship restarts for the last quarter of the graph. It seems this happens below a certain "load" value. If that matters, when the CPU is fully used (with the current power management settings) frequency is at some intermediate level:

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What is the technical explanation for how speed is managed, and how power selected management strategy is taken into account here?

Reference to Intel or general documentation preferred to guesswork 😉

Questions I have read before asking:

Using W7 on Lenovo W510 (720 QM, i7 family).

Best Answer

(Remark : You are showing screenshots of the Resource Monitor, not the Performance Monitor.)

CPU use : This is how much CPU is used across all cores. For example, if you have 4 cores and one of them is fully used, the total figure that you will see is only 25%.

CPU speed : Modern CPUs can vary their frequency by demand using Dynamic frequency scaling. The frequency may scale down, or for heavy loads scale up with turbo mode, by varying the voltage. In a multi-core CPU all the cores work at the same speed, so it is possible that because one core is under a heavy load that all cores will speed up.

Summary : CPU use relates to its total use across all CPU cores, while CPU speed relates to how fast the CPU's frequency is set at the moment.

One is not really connected to the other : In a 4-core computer, one core under heavy load may push the frequency to its maximum, while the usage will stay as only 25%.