Target shares in Workload Manager

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The target (or desired) resource consumption percentage for a class is determined by the number of shares it has for a particular resource.

The shares represent how much of a particular resource a class should get, relative to the other classes in its tier. A class's target percentage for a particular resource is simply its number of shares divided by the number of active shares in its tier. If limits are also being used, the target is limited to the range [minimum, soft maximum]. If the calculated target outside this range, it is set to the appropriate upper/lower bound (see Resource Limits). The number of active shares is the total number of shares of all classes that have at least one active process in them. Because the number of active shares is dynamic, so is the target. If a class is the only active class in a tier, its target will be 100% of the amount of resource available to the tier.

For example, assume three active superclasses classes in tier 0—A, B, and C—with shares for a particular resource of 15, 10, and 5, respectively, the targets would be:

target(A) = 15/30 = 50%
target(B) = 10/30 = 33%
target(C) =  5/30 = 17%

If some time later, class B becomes inactive (no active processes), the targets for class A and C will be automatically adjusted:

target(A) = 15/20 = 75%
target(C) =  5/20 = 25%

As you can see, the shares represent a self-adapting percentage which allow the resources allocated to a class to be evenly distributed to or taken from the other classes when it becomes active/inactive.

To allow a high degree of flexibility, the number of shares for a class can be any number between 1 and 65535. Shares can be specified for superclasses and subclasses. For superclasses, the shares are relative to all other active superclasses in the same tier. For subclasses, the shares are relative to all other active subclasses in the same superclass, in the same tier. The shares for a subclass one superclass have no relationship to the shares for a subclass of another superclass.

In some cases, it might be desirable to make the target for a class independent from the number of active shares. To accomplish this, a value of "-" can be specified for the number of shares. In this case, the class will be unregulated for that resource, meaning that it has no shares, and its target is not dependent on the number of active shares. Its target will be set to (resource available to the tier - the sum of mins for all other classes in the tier). This target, or actual consumption (whichever is lower) is then taken out of what is available to other classes in the same tier.

For example, assume classes A, B, C, and D have shares for a particular resource of "-", 200, 150, and 100, respectively. All classes are active, and class A is consuming 50% of the resource:

target(A) = unregulated = 100%  
target(B) = 200/450 * available = 44% * 50% = 22%  
target(C) = 150/450 * available = 33% * 50% = 17%  
target(D) = 100/450 * available = 22% * 50% = 11%

Because class A is unregulated and is consuming 50% of the available resource, the other classes only have 50% available to them, and their targets are calculated based on this percentage. Since class A will always be below its target (100%), it will always have a higher priority than all other classes in the same tier that are at or above their targets (see Class priority in Workload Manager for more information).

Note: Making a class unregulated for a resource is not the same as putting it in a higher tier. The following behaviors, listed here, are true for an unregulated class (in the same tier), and are not true if the class is put in a higher tier:
  • Because the shares are defined on a per-resource basis, a class can be unregulated for one or more resources, and regulated for others.
  • The minimum limits for other classes in the same tier are honored. Higher tiers do not honor minimums specified in the lower tiers.
  • Even in the absence of minimum limits for the classes with shares, the consumption of unregulated classes is somewhat dependent on classes with shares since they are competing for some of the resource available to the tier. Some experimentation is required to see what the behavior is with a given workload.

If the number of shares is unspecified, a default value of "-" will be used, and the class will be unregulated for that resource. Note that in the first version of WLM, the default share value, if unspecified, was 1.

The shares are specified per class for all the resource types. Shares are specified in stanzas of the shares file. For example: 
shares
classname:
   CPU      =   2
   memory   =   4
   diskIO   =   3