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Old 10-18-2007, 08:46 AM   #1
Sathya
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Question on top, ps and sar output


Hi

I have red hat AS Release 4 linux on a Sun x4600 server with Dual-Core AMD Opteron(tm) Processor 8218 (16 Processors).

When i run my application, and do a ps aux or a top on my process id, sometimes i see that the %CPU goes more than 100%. I sometimes see 1000% also. Why does the cpu utilization for the process goes more than 100%?

When i check the sar output %cpu for user remains at 12% and kernel remains as 3% when the application runs. Why is this difference in the cpu output between the two commands?

I can understand that the ps aux and top gives per process CPU utilization and sar gives over all utilization at a time. But i donot understand why per process cpu utilization goes more than 100% where as sar output remains at 12%

Please clarify

Thanks
Sathya
 
Old 10-18-2007, 02:22 PM   #2
raskin
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12% of 16 cores' power = 1.92 of 1 core's power. In multi-processor setup (or multi-core, for that matter) top gives you sum over all processors. So it can give 192% here (and it can give nearly 1600% if you manage to fully load all your cores).
 
Old 10-19-2007, 01:31 AM   #3
chrism01
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iirc, on RH systems you can run 'top', then press the 'esc' key (might be '1' key) & it'll show per cpu numbers.
Try man top
 
Old 10-19-2007, 01:58 AM   #4
Sathya
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Thank you very much for the clarification

Sathya
 
  


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