The shares for the individual LPARs are determined as described above:
1. Building the sum of the weights of all competing LPARs: 150 + 50 + 100 = 300.
2. Determination of the proportion of each LPAR through the calculation of the quotients:
- LPAR1: 150 / 300 = 1/2
- LPAR2: 50 / 300 = 1/6
- LPAR3: 100 / 300 = 2/6
3. This is then multiplied by the available CPU portion of 6 ms:
- LPAR1: 6.0 ms * 1/2 = 3.0 ms
- LPAR2: 6.0 ms * 1/6 = 1.0 ms
- LPAR3: 6.0 ms * 2/6 = 2.0 ms
However, the additional shares of CPU time are not guaranteed and can also change in every 10 ms time interval! For example, another LPAR could be activated, which of course then gets its guaranteed entitlement. Or the entitlement of a running LPAR is increased, which means that less unallocated capacity is available.
If an LPAR does not need all of its guaranteed processing units in a time interval, then the unused processing units are returned to the hypervisor, which then distributes them to other LPARs according to the above scheme.
The weight of an LPAR (uncapped_weight) can be changed dynamically at runtime. The command “lpar chproc” (change processors) can be used for this. In addition to the LPAR name, the uncapped_weight attribute is simply specified with a new value between 0 and 255:
$ lpar chproc aix05 uncapped_weight=100
$
If the value 0 is specified for uncapped_weight, the LPAR cannot receive any additional CPU shares beyond its entitlement. It then behaves exactly like an LPAR with sharing mode cap!
If the weight in a profile is to be changed, the command must be started with the “-p” option and the profile name:
$ lpar -p standard chproc aix05 uncapped_weight=100
$
Figure 5.9 shows the processor utilization of an LPAR with sharing mode uncap. The LPAR was configured with an entitlement of 0.6 (yellow line) and one virtual processor.
You must be logged in to post a comment.