This unallocated CPU time could be divided among the 3 active LPARs in order to achieve better performance. That would correspond to an increase in CPU time of 150%!
The processor sharing mode (attribute sharing_mode) can be used to configure whether an LPAR may receive shares of unallocated or unused CPU time. The following two values are possible for shared processor LPARs:
- cap: The CPU time is limited to the guaranteed entitlement. No additional shares will be allocated to the LPAR, even if available.
- uncap: In addition to the guaranteed entitlement, the LPAR can receive additional CPU shares from unused processor resources. This is the default for shared processor LPARs.
The sharing mode can be specified when creating an LPAR:
$ lpar create -m ms02 lpar12 desired_procs=2 desired_proc_units=0.8 sharing_mode=cap
.
> lpar12
$
The sharing mode can only be changed in the profile, so you cannot change the sharing mode from cap to uncap or vice versa while an LPAR is running. The easiest way to change the sharing mode in the profile is to use the “lpar chproc” command, specifying the “-p” option and the profile name:
$ lpar -p standard chproc lpar11 sharing_mode=cap
$
For the change to take effect, the LPAR must be shut down and reactivated by specifying the changed profile.
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