System Management Concepts: Operating System and Devices

WLM Class Attributes

The attributes of a WLM class are:

Class Name

Can be up to 16 characters in length and can only contain uppercase and lowercase letters, numbers and underscores ('_').

Tier

A number between 0 and 9 used to prioritize resource allocation between classes.

Inheritance

Specifies whether a child process inherits the class assignment from its parent.

Adminuser, admingroup (superclass only)

Used to delegate the administration of a superclass.

Authuser, authgroup

Used to delegate the right to manually assign a process to a class.

Resource Set

Used to limit the set of resources a given class has access to in terms of CPUs (processor set).

Tier Attribute

Tiers are based on the importance of a class relative to other classes in WLM. There are 10 available tiers, from 0 through 9. Tier value 0 is the most important; the value 9 is the least important. As a result, classes belonging to tier 0 get resource allocation priority over classes in tier 1; classes in tier 1 have priority over classes in tier 2, and so on. The default tier number is 0.

The tier applies at both the superclass and the subclass level. Superclass tiers are used to specify resource allocation priority between superclasses. Subclass tiers are used to specify resource allocation priority between subclasses of the same superclass. There are no relationships between tier numbers of subclasses for different superclasses.

Inheritance Attribute

The inheritance attribute indicates whether a child process should inherit its parent class or be classified according to the automatic assignment rules upon the exec subroutine. The possible values are yes or no. The default is no.

This attribute can be specified at both superclass and subclass level. For a subclass of a given superclass:

• If the inheritance attribute is set to yes at both the superclass and the subclass level, then, upon exec(), a child of a process in the subclass will remain in the same subclass.
• If the inheritance attribute is yes for the superclass and no (or unspecified) for the subclass, then, upon exec(), a child of a process in the subclass will remain in the same superclass and will be classified in one of its subclasses according to the assignment rules for the superclass.
• If the inheritance attribute is no (or unspecified) for the superclass and yes for the subclass, then upon exec(), a child of a process in the subclass will be submitted to the automatic assignment rules for the superclasses.
  • If the process is classified by the rules in the same superclass, then it will remain in the subclass (it will not be submitted to the subclass's assignment rules).
  • If the process is classified by the superclass's rules in a different superclass, then the subclass assignment rules of the new superclass are applied to determine the subclass of the new superclass the process will be assigned to.
• If both superclass and subclass inheritance attribute are set to no (or unspecified), then, upon exec(), a child of a process in the subclass will be submitted to the standard automatic assignment.

localshm Attribute

The localshm attribute can be specified at the superclass and the subclass levels. It is used to prevent memory segments belonging to one class from migrating to the Shared superclass or subclass when accessed by processes in other classes. The possible values for the attribute are yes or no. A value of yes means that shared memory segments in this class must remain local to the class and not migrate to the appropriate Shared class. A value of no is the default when the attribute is not specified.

Memory segments are classified on page faults. When a segment is created, it is marked as belonging to the Unclassified superclass. On the first page fault on the segment, this segment is classified into the same class as the faulting process. If, later on, a process belonging to a different class than the segment page faults on this segment, WLM considers whether the segment needs to be reclassified into the appropriate Shared class (superclass or subclass). If the faulting process and the segment belong to different superclasses, one of the following occurs:

• If the segment's superclass has the localshm attribute set to yes, the segment remains in its current superclass. If the segment's subclass has the localshm attribute set to yes, the segment remains in its current subclass. If the superclass localshm attribute is set to yes but its subclass attribute is set to no, it goes into the Shared subclass of the current superclass.
• If the segment's superclass has the localshm attribute set to no, the segment goes to Shared superclass. This is the default action.

If the faulting process and the segment belong to different subclasses of the same superclass, and the segment's subclass has the localshm attribute set to yes, the segment remains in the current class (superclass and subclass). Otherwise, the segment goes to the Shared subclass of the superclass.

Of course, if the faulting process and the segment belong to the same class (same superclass and same subclass), the segment is not reclassified regardless of the values of the localshm attributes.

adminuser, admingroup Attributes

Note: These attributes are valid only for superclasses.

The adminuser and admingroup attributes are used to delegate the superclass administration to a user or group of users:

• adminuser specifies the name of the user (as listed in /etc/passwd) authorized to perform administration tasks on the superclass.
• admingroup specifies the name of the group of users (as listed in /etc/group) authorized to perform administration tasks on the superclass.

Only one value (user or group) is allowed for each attribute. Either of them, none, or both can be specified. The user or group will have authority to do the following:

• Create and delete subclasses
• Change the attributes and resource shares and limits for the subclasses
• Define, remove or modify subclass assignment rules
• Refresh (update) the active WLM configuration for the superclass.

Note: The root user always has authority on any superclass.

authuser, authgroup Attributes

The authuser and authgroup attributes are valid for all classes. They are used to specify the user or group authorized to manually assign processes to the class (superclass or subclass). When manually assigning a process (or a group of processes) to a superclass, the assignment rules for the superclass are used to determine to which subclass of the superclass each process will be assigned.

Only one value (user or group) is allowed for each attribute. Either of them, none, or both can be specified. In addition, the root user and the administrators of a superclass specified by adminuser or admingroup can always manually assign processes to a superclass or to a subclass of the superclass.

Resource Set Attribute

The resource set attribute (called rset) is valid for all the classes. Its value is the name of a resource set defined by the system administrator. The rset attribute represents a subset of the CPU resource available on the system (processor set). The default is "system," which gives access to all the CPU resources available on the system.