Over AIX 6.1 - I do see the following output, it says I have 16 Max Physical CPUs; but there are only 8 active - why is that?

The system will use the remaining 8 if needed?
Or are they disabled?

# lparstat -i | grep CPU

Online Virtual CPUs                        : 8
Maximum Virtual CPUs                       : 8
Virtual CPUs                               : 1
Maximum Physical CPUs in system            : 16
Active Physical CPUs in system             : 8
Active CPUs in Pool                        : -
Shared Physical CPUs in system             : -
Physical CPU Percentage                    : 100.00%
Desired Virtual CPUs                       : 8

Here I can see there are 16 available.

# bindprocessor -q
The available processors are:  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
  • Hi - would be possible to elaborate? I don't really catching your questions. Thanks!
    – Andres
    Jan 21 '15 at 21:37

A couple of reasons for having less active CPU's than available are:

  1. IBM POWER servers have something called capacity in demand, which means that you can buy a server with more CPU's installed than want to use initially, and activate them later when needed. Like in your case the servers has 16 CPUs installed, but only 8 are active.

  2. Another reason for inactive CPUs can be a hardware problem. Lets assume your server doesn't have extra CPUs because of capacity on demand. It is possible that if a hardware error occurs on the CPUs or CPU boards, the server will deactivate them to prevent corruption.

  • For number one, is it an energy consumption thing?
    – Bratchley
    Apr 17 '15 at 4:53
  • 1
    No, it is more for expedience and possible avoidance of downtime. If you already have the CPUs installed but disabled, when you need them you just need to contact IBM, place an order to activate more CPUs or memory (this works for memory also), and after your order is processed they just give you a key to enter in your server to enable additional CPUs/RAM. No downtime to install them, and you can have then available very quickly. There several other options for capacity on demand, for more info [link](www.ibm.com/systems/power/hardware/cod/)
    – jgruiz
    Apr 17 '15 at 11:19
  • So...literally downloading more RAM.
    – Bratchley
    Apr 17 '15 at 12:37
  • Good way to look at it for sure!
    – jgruiz
    Apr 17 '15 at 12:41

I know this is an old post, but to confirm, the bindprocessor command will show the number of logical CPU's which is the number of Virtual CPU's (in this case 8) multiplied by the processor simultaneous multithreading (SMT) setting, in this case the server is running SMT2, so it is VCPUxSMT=LCPU. Use the smtctl command, as root, to check the current SMT setting on the LPAR.

vmstat command will also show the number of logical cpu's.

The "Maximum Physical CPUs in system" in the lparstat command is the number of configured CPU's on the server which is available to all LPAR's.

  • Welcome to the site, and thank your for your contribution. Could you add links to man-pages or other resources as references for the explanation?
    – AdminBee
    Sep 23 at 14:01

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