CPU Usage at 100% with nothing appearing as running RRS feed

  • Question

  • I am having a problem with a laptop running XP Pro where the CPU usage stays at 100% in task manager > Performance.  When I look in Task Manager Processes there is nothing but system idle process using CPU.  How can I see why it says it is at 100% CPU usuage and what is using the CPU.  The computer does not run slow or seem impeded at all.  Any help is appreciated.

    Wednesday, September 9, 2009 7:16 PM

All replies

  • Hi harmon808,

    Since you're running XP... Please download Process Explorer and run it, and sort the CPU column in descending order.  My guess is you will find that Interrupts or DPCs are responsible for the CPU usage...
    Wednesday, September 9, 2009 11:02 PM
  • Download Process Explorer from

    Process Explorer - DPC

    and if you see a heavy CPU/CSwitch (Context Switch Delta) activity then - "No.Compromise " guess will be correct.

    Then you will have to use xperf with Latency (Kernel group - PROC_THREAD+LOADER+DISK_IO+HARD_FAULTS+DPC+INTERRUPT+CSWITCH+PROFILE) flag to capture the events and the analyze with xperfview - DPC & Interrupt CPU Usage Summary Table

    Note: "A driver should spend no more than 25 microseconds in an ISR and no more than 100 microseconds in a DPC." - Check for Avg Actual Duration that exceeds 100 microseconds and dig deeper in to the module that’s causing the problem. Same with ISR, check for Avg Actual Duration that exceeds 25 microseconds in Interrupt CPU Usage Summary Table

    Siva Mulpruu
    • Proposed as answer by Smulpuru Monday, September 14, 2009 3:03 PM
    Monday, September 14, 2009 3:02 PM
  • Don't sweat the xperf stuff until you've determined using Process Explorer that interrupts or DPCs are in fact involved, however...  In fact, you're running XP, and xperf / WPT won't do much good there...
    • Proposed as answer by No.Compromise Tuesday, September 15, 2009 1:06 AM
    Monday, September 14, 2009 4:45 PM