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Running Windows XP on a AMD dual core processor. Occasionally after booting, logging on, and letting things settle down, the Task Manager shows on the graph that one processor is over 90% busy. Yet when one looks at processes running, system idle is at running around 98%. On performance graphs, the CPU usage bar shows as red with tiny amount of green. Only one user is logged on.

It is as though there is a rogue task that task manager doesn't know about when showing the processes, but does know about when showing the performance graphs.

I have seen this several times. What I've done in the past is reboot the system, and the problem/anomaly was no longer present. A log-off / log-on did not get rid of the rogue usage.

I have not explored if the issue is triggered by a long delay from power-up to log-on.

System seems clean on anti-virus scans. Network activity is zero.

Any ideas as to what might be happening?

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migrated from Oct 22 '09 at 18:35

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Process Explorer provided additional information. System Idle Process dropped to just under 50%. About 30 to 35% of CPU for Hardware Interrupts (?!) and 8 to 12% showing as Deferred Procedure calls. – Anonymous Oct 21 '09 at 21:23
Ran RATTV3. nvata.sys seemed to have high numbers with DPC Total 33 million in 3 runs, next highest at 35k. Rebooted system, problem now not present. Thought I could do a compare, but the histogram is cumulative. RATTV3 says after 13 runs, nvata.sys at 42 million. I would guess almost all of that was pre-reboot. – Anonymous Oct 21 '09 at 21:24
Unsurprisingly, it's a video card driver. Make sure you've got the latest stable version of the drivers. – user3463 Oct 22 '09 at 8:45
I refreshed the drivers on Oct 21 (now at AKA 191.07). So far no recurrence. – refactor Oct 27 '09 at 15:01
Its back. RAATV3 shows nvata is at it again. 191.07 is still current set of nvidia drivers. – refactor Nov 6 '09 at 0:30
up vote 0 down vote accepted

I'd try googling for the sysinternals suite and run process explorer to see if that can give more information on what is running on the processors.

Failing that you can also run process monitor and that will tell you what processes are issuing file and registry I/O and see if something there is constantly busy (use the autoscroll option from the menus to see real-time changes).

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I didn't think process explorer would say more, but a download and execution proved otherwise. System Idle Process drops to just under 50%. About 30 to 35% of CPU is Hardware Interrupts (?!) and 8 to 12% showing as Deferred Procedure calls. – Anonymous Oct 21 '09 at 19:55
If you haven't used it before, ProcExp has a lot of neat nuggets of features if you explore using right-click and menus. Lots of inside information. – Bart Silverstrim Oct 21 '09 at 20:02
Sounds like you might want to check around for I/O, to see what is issuing the interrupts. HD? Network card? There may be another sysinternals tool that will tell you more... – Bart Silverstrim Oct 21 '09 at 20:09
This might – Bart Silverstrim Oct 21 '09 at 20:10
Any of these might also lead to some clues.… – Bart Silverstrim Oct 21 '09 at 20:12

It's a kernel space thread taking up that CPU. They show up as red if you have 'Show System Kernel Times' turned on in the menu

(It may not be exactly that, but I'm not sitting in front of a Windows box at the moment)

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Yes it is. So what? What is the importance of the fact that it's all kernel activity? It's definitely not normal for the OS kernel to consume 50% of the processor "just because". – Task Aug 27 '12 at 15:47

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