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Thread: Problem with ACPI.sys and DPCs/Interrupts causing pegged CPU.

  1. #1
    Join Date
    Dec 2007

    Problem with ACPI.sys and DPCs/Interrupts causing pegged CPU.

    My computer has an Intel I7-920, which gives me up to 8 cores (4 physical + 4 virtual). I run windows vista 64bit. I noticed while playing wow that I would get periods of choppy'ness and the speakers would emit static. When looking at the task manager, I noticed that CPU3 was pegged at 100%.

    I was able to work around WoW by setting its processor affinity to CPU6 and CPU7, but the sound is still affected. The processor isn't always pegged to full. It happens in spurts.

    I managed to log a small session of it using xperf from the microsoft SDK tools. The overwhelming problem seems to be from ACPI.sys causing interrupts and generating large amounts of DPCs (Deferred Procedure Calls).

    This was the xperf output charts (top chart is strait up CPU3 usage):

    DPC stats for the first 3 minutes of logging:

    Interrupt stats for the first 3 minutes of logging:

    If anyone could give some help/guidance, I would appreciate it. I am not sure if I can disable ACPI.sys and what the implications are. I would prefer to fix it if possible (or if this is actually a hardware issue, how do I tell?).


  2. #2
    Join Date
    Apr 2008
    DO NOT disable ACPI. Well.. not yet.

    ACPI stands for Advanced Configuration and Power Interface, and basically has complete control over how power flows throughout your system. ACPI.sys is the Windows process that plugs into the hardware ACPI to help control hardware level power functions. Basically it is a bridge that allows the software drivers (some software drivers, other software drivers plug directly into the hardware ACPI, especially video card drivers) to talk to certain parts of the hardware in your computer. It controls things such as throttling programs back when the CPU gets to hot, or increasing the fan speed, and turning off certain hardware when the computer enters sleep mode. It even will shut down DirectX when it detects that your video card is getting too hot.

    I am not sure what would happen if you disable ACPI.sys, as I am only familiar with the hardware side of the ACPI, as well as the Unix ACPI, but my gut says it is a bad thing. Maybe someone will show up that has more experience with the Windows ACPI.

  3. #3
    Join Date
    Jul 2009
    You cannot disable ACPI. To "disable" it, you will need to completely reinstall your OS with ACPI turned off, otherwise disabling it will make your pc unbootable. As for CPU3 Pegging, can you provide us with some taskmanager info as to which process is pegging your CPU.

  4. #4
    Join Date
    Dec 2007
    The task manager never showed any processes with high cycles/usage. I actually ended up having to use xperf to find the acpi.sys and interrupt problem because taskmgr acted as if everything was fine (minus the graph showing CPU3 at 100%).

    I managed to fix it I think. I am watching things. I opened up the box and reseated a bunch of stuff and went ahead and can'o'aired the sucker to be safe. So far everything is working smoothly.

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