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Why is nmon showing 8 CPU when I have 4 physical CPU and no partitions?

Posted on 2007-11-13
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nmon when run on AIX 5.x is showing 8 CPU on a 4 way non partitioned box.  Our 8 way is showing CPU of 16 when viewed with nmon.  Can anyone explain to me why this is?
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Question by:Angela_Wilcox
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4 Comments
 
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Expert Comment

by:sjm_ee
ID: 20278451
Is SMT on? Run "smtctl" to see if it is. What do the first 40 or so lines of "prtconf" say?
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by:dfke
ID: 20279291
Yes, this is due to the SMT feature of the POWER5 chip, where each CPU (core) runs two processes at the same time.

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by:Angela_Wilcox
ID: 20288386
Could it also be a result of our 64 bit upgrade - which I did not know we had done??
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dfke earned 1200 total points
ID: 20297863
No it's really due to the SMT feature on the chip.

SMT, or Simultaneous Multi-threading is a hyperthreading design. Somewhat like Intel's Pentium 4 HT. Which also doubles the amount of cpus in Windows. It makes each core capable of running two threads at once.  The OS "sees" the SMT feature as a logical cpu apart from the physical cpu or core if you will.

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