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Old 01-02-2013, 01:41 AM   #1
tarunkumar
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Is there limitation on %CPU


Hi All,

My server has 80 core and with hyper threading 160. There is a heavy application running on the system.At times when the system is slow when i see the top command the CPU utilization will be 9999%. when i see the 9999% CPU utilization the system response is very bad, but as i understand 9999 means only 100 CPU threads. Is there a limit of number 9999 for the CPU utilization in top command??.

Regards,
Tarun.
 
Old 01-02-2013, 02:15 AM   #2
syg00
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Could be just a display limitation (hopefully). Try "Irix" mode - (use the "I" toggle); if the accumulator field is sufficiently wide you'll get a normalised CPU%.
A quick perusal of the source will be definitive.
 
Old 01-02-2013, 09:22 AM   #3
jpollard
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It is a format overflow...

There are only 4 columns available in a nn.n format. I believe top is truncating the string value after conversion (taking the last 4 digits from the string buffer- you would have to look at the source to see exactly how though).

The maximum is of course 100%, but the display would need 100.0 (5 columns) which is never actually reached except when there are measurement errors (you can actually exceed 100% because one process may reach 100% during its time quantum... then it switches to top which captures it, then switches to another process which tops out, then switches back to top which captures that one... So the sum would exceed 100%. Doesn't happen very often though.
 
Old 01-02-2013, 11:24 AM   #4
tarunkumar
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Thanks syg00 and jpollard. Have you ever saw CPU% displaying more than 4 digits.

Thanks,
Tarun.
 
Old 01-03-2013, 06:22 AM   #5
jpollard
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I've seen 100+, but not using top, and it has been a long time since (it was on a single CPU system - all my systems since Pentium level have been duals).
 
  


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