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Old 05-06-2011, 06:40 PM   #1
andrews-mark
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big cpu usage, but top shows no heavy use process


Hi all,
I have been running to a strange problem. For a few days, a few times a day something seems to take over my machine. Suddenly I can't type, or the key shows up about 5 seconds are being pressed, music players halt, etc.
In anticipation, I had top and htop running. Sure enough, when this business begins htop reports all 8 cores firing at near 100% for a few minutes. However, top is telling me nothing about who is too blame. The cup%sy on top shows heavy usage, but the top processes are nothing remarkable, mostly just top and htop and conky, all running at around 1 or 2% on average.
I am a bit puzzled as to why I can't see the cpu hog so that I figure out what is going on.
My question then: Are there some processes (in kernel space?) that don't show up in top, yet which could be hogging the cpu?
gracias,
-m
 
Old 05-06-2011, 11:44 PM   #2
syg00
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Quote:
Originally Posted by andrews-mark View Post
My question then: Are there some processes (in kernel space?) that don't show up in top, yet which could be hogging the cpu?
Certainly - %sy is "system mode" time.
Not (generally) processes as such, but maybe interrupt handlers or dodgy drivers. Probably the latter - changed anything recently ?.

Diagnosis can be a mongrel - try removing/not starting devices until things recover. Might toss up a suspect.
 
Old 05-10-2011, 11:46 AM   #3
andrews-mark
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syg00 - Thanks for your advice. I did change a lot on the system recently, in particular added ltsp, so it is not easy to narrow down the hog. However, and oddly, since last reboot, there is been no repeat of this incident, so I may have got lucky.
-m
 
Old 06-21-2011, 09:22 PM   #4
andrews-mark
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After weeks of some strange system process sporadically showing up and taking over the machine for around 15 minutes each time and then dying down again, I eventually tracked it down as due to the second ethernet card I recently put in. This was a cheap old thing. I replaced it with a proper one, and all is quiet again.
The following site was extremely helpful for the diagnosis:
http://honglus.blogspot.com/2010/01/...cpu-usage.html
 
Old 04-13-2012, 01:22 AM   #5
scipilot
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FYI. I had this behaviour on a virtual Centos 5 box - and it was because VMWare tools wasn't running properly.

Just loading one simple web page caused the user cpu to reach 100% for 30 seconds+, but the one or two httpd processes were only showing 2 or 3% in top and certainly not adding up to 100%! I then noticed that VMWare wasn't allocating extra cpu Mhz when the guest hit 100% and checked vmware tools - which had died.

After re-installing VMWare tools and updating the drivers with vmware-config-tools.pl, it all started to behave normally again. Pages now load in milliseconds and VMWare is ramping the Mhz up to a gig as needed.
 
  


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