Double No.of CPU's shown by nmon10 on AIX 5.3 ML8 SP3


 
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Operating Systems AIX Double No.of CPU's shown by nmon10 on AIX 5.3 ML8 SP3
# 1  
Old 04-05-2009
Question Double No.of CPU's shown by nmon10 on AIX 5.3 ML8 SP3

Hi all,

We are recently migrated to AIX 5.3 ML8 SP3 on pseries systems,when we run the nmon we noted that the nmon display doubled no. of CPU's i.e we have physically 8 CPU's on p570 machine but nmon displays 16. Is this a bug of this version or what?

Thanks in Advance
# 2  
Old 04-05-2009
Hi,

I assume you migrated from an earlier AIX version like 5.1 or 5.2?

What you see is not a bug, its a feature. Nmon is showing LCPUs. This is because you are getting the OS (AIX or Linux) to run twice the number of processes/threads at the same time if you make use of the SMT feature of the POWER5 and POWER6 processors which can concurrently execute instructions for two processes in the same clock cycle on different units inside the processor - and you usually do.

Kind regards
Nicki
# 3  
Old 04-06-2009
with smtctl you can verify this setting and turn smt on or off. No reboot required
# 4  
Old 04-07-2009
Thanks Nicki & raba

The same nmon problem we noticed on another machine which was also migrated to 5.3 with same ML8 & SP3, but yesterday we applied SP5 on that machine and we noticed that after applying the SP5 the nmon now shows exact no. of CPU's as they are physically on system.

Now what I understand is that in SP3 the SMT feature is enabled by default, but in SP5 we have to activate or ON this SMT feature.
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