4 Replies Latest reply on Sep 4, 2013 11:25 AM by kevin_intel

    Multiplicator step up / down thresholds

    ThunderBlade

      Hi,

       

      from what I understand, Intel SpeedStep works this way:

      - upon a certain CPU load, the multiplicator is switched up to the next available one.

      - below a certain CPU load, the multiplicator is switched down to the next available one.

       

      What I don't understand are the CPU load tresholds and times that are used. Using "CoreTemp" under Windows 7, I can see the switching happening. It seems that only after a certain time of a certain CPU load, my i5 switches up from 1.2 GHz to 1.4 GHz, and so on. Also when load is 2% or lower, after a certain time (a few seconds?) it switches down.

       

      1) Is there a document listing the CPU load tresholds and times that are defined for switching multiplicator up/down?

       

      2) Is it possible to change the load or time tresholds with a kind of (yet to be written) software configuration utility? E.g. to enhance battery life, I might consider upping the mulitplicator only when the load exceeds, say, 50%, and not just 5% or so. Also I might consider CPU peaks of less than say, 3 seconds, to be ignored when I am on battery. etc. This was possible under Windows XP with the tool "Notebook Hardware Control", but it doesn't work on Windows 7.

       

      Thanks,

       

      - ThunderBlade

        • 1. Re: Multiplicator step up / down thresholds
          ThunderBlade

          I would have expected that someone more knowledgeable than me would answer.

           

          After some long digging, I found the solution. Windows 7 reads the information in question out of so called ACPI tables, provided by the BIOS. It then uses them according to its internal policies, but you can change it.

           

          From a cmd.exe with Admin priviliges, do:

           

          powercfg -attributes SUB_PROCESSOR 4d2b0152-7d5c-498b-88e2-34345392a2c5 -ATTRIB_HIDE

           

          After this you suddenly will find a new option in Energy Management under Processor Energy Managment. It will allow you to change the interval the need for a switch up or down is evaluated. On my machine the default was 30 milliseconds. I changed it to 100 milliseconds and voila: I see the machine switch up less often. Before, even on an "idle" system, it switched up from time to time because of some background processes.

          • 2. Re: Multiplicator step up / down thresholds

            Hi Thunderblade.

             

            You are on the right track, but one small correction to your original post.  Enhanced Intel SpeedStep® Technology doesn’t change the multiplier, it changes the P-State of the processor.  A P-State is specified combination of voltage and frequency.

             

            P-states cannot be modified (meaning you can’t change the voltage/frequency combination for say P-1), but you can modify how aggressively the OS manages the transitions.  Microsoft® has a very good article here:  http://download.microsoft.com/download/3/0/2/3027D574-C433-412A-A8B6-5E0A75D5B237/ProcPowerMgmtWin7.docx.

             

            You will find a list of Processor Power Management settings starting on page 27.  You will need to use Powercfg.exe to un-hide some of them using the same general syntax you noted in your second post.

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            • 3. Re: Multiplicator step up / down thresholds
              ThunderBlade

              Hi Kevin,

               

              thanks so much for following up. I had meanwhile found a similar document from Microsoft (probably an older version), and I have been experimenting with the settings to influence the transition through the P-States. The default settings seem to assume a totally idle CPU, that switches up as soon as e.g. an MP3 player is active in the background, or a website uses an annyoing flash advertisement. That naturally consumes more power and heat. The most important setting seems to be the "Processor Performance Increase Threshold", increasing it helps avoiding a switch up on minor CPU load peaks.

               

              On my i5 the lowest state is 1.2 GHz. I wonder if it is possible to go below that, e.g. 1.0 GHz or 800 MHz, on very low CPU loads?

               

              Cheers,

               

              - ThunderBlade

              • 4. Re: Multiplicator step up / down thresholds

                Hello ThunderBlade,

                 

                It is possible to change it but not recommendable since the processor can be damaged by going below the normal states.