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Hidden CPU utilization?

  1. Jul 21, 2008 #1

    CRGreathouse

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    I'm running Windows XP on a dual-core notebook and I noticed that sometimes (like now ;)) the computer slows down dramatically as though under heavy load, but the task manager reports nothing: the system idle process claims 97% of the CPU and there's only ~500 MB of RAM in use (on a 2 GB system). But the fans run loudly, and the task maanger does report (in a contradictory way) that CPU usage is about 55%.

    Any thought? I do have "show processes from all users" checked.
     
  2. jcsd
  3. Jul 21, 2008 #2

    robphy

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  4. Jul 22, 2008 #3

    Borek

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    It is just a wild guess, but if the fans run, perhaps your notebook is overheated so it automagically slows down? I was never interested in details but some processors (especially those targeted at notebooks) have fancy solutions implemented to save on energy and to diminish chances of overheating.
     
  5. Jul 22, 2008 #4

    CRGreathouse

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    The laptop does have automagic slowdown (Intel's SpeedStep), but it wasn't on at that time.

    Process Explorer may have found the problem. For a decent chunk of time, maybe two minutes, there was 40-50% CPU use for "hardware interrupts". Should they really take that much juice?
     
  6. Jul 22, 2008 #5

    robphy

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    On occasion, I have an issue with my setup in which the Bluetooth drivers are trying to install devices it detected [which I don't want it do]. This eats up my CPU time as it struggles to install these devices. So, I have to manually kill off the process. (If I allow it to finish, the install eventually fails.... so I kill it off early.)

    So, something like this might be an issue.
    Is there a particular process that is using up the CPU? Process Explorer can help identify the process.
     
  7. Jul 22, 2008 #6

    CRGreathouse

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    Process Explorer calls the process that I identified above "hardware interrupts".
     
  8. Jul 22, 2008 #7

    robphy

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  9. Jul 22, 2008 #8

    CRGreathouse

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    Thanks, I'll look into that.
     
  10. Jul 22, 2008 #9
    Since you have two CPUs that likely means that one of the cores is running 100% running a single threaded job.
     
  11. Jul 22, 2008 #10

    CRGreathouse

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    Yes, certainly. That's why I mentioned that I was a running dual-core.
     
  12. Jul 22, 2008 #11

    CRGreathouse

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    That did it for me! Or at least found the problem, which I trust I can fix. My hard drive went from DMA to PIO mode, so every time I used the hard drive everything slowed down.

    I'm playing with
    HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\Scsi\Scsi Port 0\DMAEnabled
    now; hopefully this works.
     
  13. Jul 22, 2008 #12

    CRGreathouse

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    OK, it's solved. I deleted the driver for the primary IDE and rebooted twice. Now the hard drive is back to DMA and the computer is running at least four times faster.

    Thanks a lot, robphy!
     
  14. Jul 22, 2008 #13

    mgb_phys

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    There is a 'feature' of windows from XP onwards, after a certain number of drive errors it automatically switches to PIO mode.
    This is a problem with DVDs, if you play a badly scratched disk it assumes the errors are due to the drive and switches to PIO which is often too slow to play movies.

    See http://sniptools.com/vault/getting-back-to-dma-mode-in-windows-xp to fix it.
     
  15. Jul 22, 2008 #14

    russ_watters

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    Ouch, that's good to know - I noticed my dvd drive running rediculously slow a few months ago and found it in PIO mode. Gotta love MS! What they should do instead is slow down the rotation of the disk, try to read the area a few times at a lower speed, then decide it is a disk error.
     
  16. Jul 23, 2008 #15

    CRGreathouse

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    Yes, this is an intentional feature -- though I thought it started in Win2000, not XP. Regardless, I happened to try that set of steps (though I didn't read that page) and they failed for me. Only deleting the driver worked.
     
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