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I am using a VisualVM which is a Java Virtual Machine profiler. I am trying to start the application jvisualvm and it giving the message

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I am working on a Sony Vaio laptop model number VPCEA24FM which has a Intel Core i3 processor.

My Question

How to find out if my CPU uses dynamic CPU frequency switching and if yes should I turn it of and what will be trade off and how?

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2 Answers 2

up vote 5 down vote accepted

Yes, all Core CPUs use dynamic CPU frequency switching which Intel calls SpeedStep.

You can enable or disable it in your BIOS (where it may be called EIST).

If you want to see if it's enabled without rebooting, use a program like CPU-Z and watch what happens as the processor load changes.

Here's my system idling:
idle

Here it it is running the benchmark in the 7-Zip GUI:
load

Notice how the Core Speed and Multiplier (and voltage) dynamically change based upon the CPU's load.

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While the excellent answer from Louis answers the how-to-find-out part of the question, I don't think it answers the other part.

Dynamic CPU frequency (and core-voltage) switching permits the CPU to work only as much as it needs to, thus saving energy. This becomes extremely critical feature on Laptops, where energy savings translate into longer period of usage without the need to recharge. Also less frequent battery recharges, means a higher battery life.

Without CPU frequency switching, the power consumption remains almost constant (variations coming from peripheral usage, e.g. hard-disk spinning or not, CDR-drive being in-use or not etc. Another big benefit of frequency switching is to reduce heating, and as a result fan-speed and as a result noise level.

In a nutshell, unless your computers' workload is fairly constant, you are on grid-power and need to frequently run tools (s.a. the performance measurement tool) that depend on fixed frequency -- you should have the dynamic frequency switching enabled.

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