WLM monitors and regulates the CPU utilization and physical memory consumption of the threads and processes active on the system. You can set minimum or maximum limits by class for each resource managed by WLM. In addition, a target value for each resource per class may be given. This target is representative of the amount of the resource that would be optimal for the jobs in the class. The processes are automatically assigned to a class by WLM upon execution, using a set of class assignment rules provided by the system administrator.
The different resources can be limited by the the following values:
Resource limit values are specified in the resource limit file by resource type within stanzas for each class. The limits are specified as a minimum to maximum range, separated by a hyphen (-) with whitespace ignored. Each limit value is followed by a percent sign (%).
WLM does not place hard constraints on the values of the resource limits. The following are the only constraints:
WLM enforces the maximum range to ensure that a class or process within a class is not given more resource than the specified value. Note that in the case of a memory constraint, swapping performance can become very poor for processes within the constrained class. Memory minimums for other classes should be used before imposing a memory maximum for any class.
A minimum value constraint on a class means that processes within the class are always allowed to get resources up to the minimum. WLM cannot guarantee that processes actually reach their minimum limit. This depends on how the processes use their resources and on other limits that may be in effect. For example, a class may not be able to reach its minimum CPU entitlement because it cannot get enough memory.
The target for use of different types of resources is specified by shares. The shares are specified as relative amounts of usage between different classes. If unspecified, the default share is 1. One way of thinking about shares is as a self-adapting percentage.
For example, a system has 3 classes, A, B and C defined, whose targets are respectively 50, 30 and 20.
If all 3 classes are active, the total number of shares for the active classes is 100. Their targets, expressed as percentages is 50%, 30% and 20%
.If A is not active, the total number of shares is 50 (so each share represents 2%). The target percentages for B and C are 60% and 40%.
If only one class is active, its target is 100%.
In this example, the sum of the shares for the 3 classes was 100 simply to make the sample calculation easier. A target can be any number between 1 and 65535.
The target represents a percentage of resources, which can vary widely, depending on how many classes are active at any given time. However, WLM makes sure that the dynamic value of the target remains compatible with the minimum and maximum values for the class. If the calculated percentage is below the minimum, WLM uses the minimum as the target. If the percentage is above the maximum range, WLM uses the maximum as the target. If the percentage is between the minimum and maximum, WLM uses the calculated value.
The tier value for a class is the importance of the class relative to other classes. The tier value 0 is the most important; the value 9 is the least important.