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Thread: Speedstep and C-States not working properly on Windows 7




  1. #1
    Join Date
    Oct 2015
    Location
    Oz
    Posts
    8

    Default Speedstep and C-States not working properly on Windows 7

    Am hoping some windows guru may be able to help me with my current problem. My initial problem(high cpu temps) was something I thought was hardare-related(see Replacement heatsink+fan for Core100HT-BD), and thanks to the help there, have managed to resolve the hardware side of it. Now, I think the rest of the problem is software-related, specifically Windows 7.


    My problem is that with my current windows install, the cPU never clocks down(or whatever its called when Intel Speedstep is active and the cPU doesn't run at full speed) or enters into C states(for energy savings and subsequent temp decrease). Over the past few years I've had the machine, I've been tweaking stuff here and there so I must have done something to the setup of windows which has caused this and I don't know what it was that caused it as I've only just noticed the results. I've been using CPU-Z and RealTemp TI to check the current speed of the CPU and also whether or not it enters into C-States. Lets call this Setup 1, my current setup that isn't 100% working right.


    Reason why I'm pretty sure its a software issue, and not a hardware issue, is because I've got an image of my SSD from when I first set it up(around 2010/2011?), and when i've installed this image onto another HD and booted off this image, the CPU clocks down and enters into C3 when the computer is idle, will call this Setup 2. BIOs settings have been unchanged from my current settings (EIST, Speedstep, and C-States are all enabled in the BIOS in both instances), so its something software related, probably Windows as not much other software has been installed on the box since then, its a HTPC which I primarily use XBMC/Kodi on. which is why I've been tweaking the system for low latency, etc... which is probably the initial cause of this issue


    So main difference between Setup 1 and Setup 2 are some tweaks to Windows that I've done in the intervening years, and I can't figure out which is the tweak which is breaking Speedstep+C-States. One thing I have noticed is that on Setup 1, if I disable C-States on the BIOS, then the CPU will clock down as expected(ie. Speedstep is working) when idle, but obviously never enters into any C-States as it has been disabled. So it looks like C-states has been disabled on my Windows OS somewhere, and this is somehow also causing Speedstep to also not work properly. Once I disable C-States on BIOs, then the Speedstep is free to work properly again.


    In both setups, Power Management has been set to "High Performance", with MinimumProcessorState=5% and MaximumProcessorState=100%. I've even exposed the all hidden settings(eg. stuff like ProcessorIdleDisable, etc) within the power plans to compare them and they're all the same. Have also tried restoring default settings for the plan and no difference. The registry entries for Processor and Intelppm are both still set to the default setting of 3, so its not that. I've also tried setting the Power Management to Balance or Power Saver, and still no change.


    So, given all that information, can anyone suggest any other thing I can check/change to get both speedstep+C-States working on my current install? I would rather not re-install windows.

  2. #2
    Join Date
    Oct 2015
    Location
    Oz
    Posts
    8

    Default Re: Speedstep and C-States not working properly on Windows 7

    Just an update for others who may run into a similar problem. After A LOT of troubleshooting, I managed to find the root cause of my issue. Noticed that when I ran MSCONFIG and ran selective boot with only essential services, etc that it seemed that the CPU was clocking down properly, etc. Did some systematic testing(enabled each service one at a time, etc..) until I had isolated the service that seemed to be causing it. Both "Multimedia Class Scheduler" and "Windows Audio" seemed to be the services, that once they were started, would cause the issue. After further research, I found out that "Multimedia Class Scheduler" was a dependency of "Windows Audio", so that was the primary culprit. I also did another test, disabling the audio drivers on Device Manager, and that also fixed it.

    As I needed audio drivers to be working(it was a HTPC), I uninstalled the audio drivers, cleaned it out, and re-installed the latest audio drivers. Now, with the audio drivers enabled and the services I mentioned above all enabled and started, my CPU was clocking down when idle, going into turbo-mode when required, dropping in C-States when idle, etc. working as it should.

    I must have played around with the audio drivers a while ago, working on either latency or multi-outputting audio to multiple devices concurrently, and that must have caused it to misbehave.

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