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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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Last Modified: 2013-11-17
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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by:sjm_ee
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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
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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
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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 300 total points
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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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