0

I realized that speed of my CPU is not constant even if it compute massively. The speed wanders from ~4,2 to ~4,4GHz in task manager. Why?

I have two theorem:

  • This is an average speed, and even during massive CPU usage there are time slots, where we wait for memory/IO, and the speed jumps back to base speed for a while.
  • The CPU main clock generated with error (jitter/wander), while the measurement using a high precise clock.
  • Other...?

enter image description here

I use Win10

0

2 Answers 2

3

Clock speed management in a modern CPU is most of all thermal management: Starting from a base frequency, that can be sustained with optimal cooling over long periods of time, the CPU can be "boosted" to higher clock speeds if either not all parts of the CPU are used (e.g. single-threaded workloads) or throttled (if the cooling is unable to remove the heat, most notoriously in Apple "Pro" Books).

Your Screenshot gives the impression of a hexacore CPU with only one core running full steam ahead. In this case the thermal management is able to boost the clock frequency from the base 3.2 GHz to over 4.2 GHz: While the one core produces a lot of heat, the others are basically idle, most likely partly switched off. This clock speed can not be sustained indefinitly, and when another core has to pick up some load (background tasks etc) the boost on the active core has to be reduced.

Since the boost/throttle are reevaluated from thermal and load datapoints many times per second (100s of times IIRC), the current clock speed will fluctate quite heavily. This is normal and to be expected.

2

Your CPU has a base speed of 3.19 GHz (probably officially reported as 3.2 GHz). When possible, it will run faster than that. What determines whether or not it's possible to run faster than that depends on the CPU's power consumption and temperature. It also depends on how many of the CPU's cores are loaded.

Most likely, your variations in speed are due to the way the work is putting load on the CPU. When it's putting load on more cores, the speed drops to keep the power consumption within the configured limits. Note that the speed it drops to is still well above the advertised base speed.

Not the answer you're looking for? Browse other questions tagged .