• 1 reply
  • Latest Post - ‏2014-07-07T07:59:00Z by Wouter Liefting
3 Posts

Pinned topic Query about Uncapped mode

‏2014-07-06T14:13:52Z |

Hi All,

I have an Shared Processor LPAR with following settings:


Total Managed System Processing Units : 8


Processing Units :


Minimum Processing Units : 0.2

Desired Processing Units : 2.5

Maximum Processing Units : 8

Virtual Processors:


Minimum Virtual Processors : 2

Desired Virtual Processors : 4

Maximum Virtual Processors : 8

Sharing Mode : UNCAPPED    Weight : 128

I would like to know in the above configuration. if there is a high CPU utilisation, whether the CPU will exceed the DESIRED Virtual Proc setting of 4 and grow up to the Maximum VP value of 8 or the CPU growth is limited to Desired Virtual Processor value of 4?

Sorry I am getting different views on this when searched in Google ...if someone clarifes would be great help...thanks a lot in advance.

  • Wouter Liefting
    Wouter Liefting
    43 Posts

    Re: Query about Uncapped mode


    You should ignore the "Minimum" and "Maximum" values during the running of the system. Those values are only important when the system boots but the "desired" resources are not available, and are the limits for DLPAR operations.

    In absence of resource constraints at boot, and in absence of any DLPAR operations, the partition will be running with the "desired" amount of resources. So your partition will have four virtual processors and an entitled capacity of 2.5, uncapped. This essentially means that the hypervisor will reserve 25 ms worth of CPU time for you in each 10 ms timeslice, and the 25 ms will be spread across four physical CPUs.

    At high CPU utilization, and if no other partitions are competing for CPU resources, then the partition can go as high as 4.0 processors (40 ms worth of CPU time in each 10 ms timeslice). Not higher than that, because AIX only sees four processors and will only schedule enough processes to fill these four CPUs. (8 processes on Power6, 16 processes on Power7, due to SMT)

    At high CPU utilization, but if other partitions are also competing for CPU resources, you will always at least be guaranteed the entitled capacity of 2.5 (25 ms of CPU time in each 10 ms timeslice). That's what the hypervisor reserved for you. Whether you can grow to 4.0 depends on the CPU utilization & weight of the other partitions, and how many processors are available in the processor pool.