Deciding about better performance for certain users and commands

You can allow individual users or groups of users to have different levels of performance than they receive by default. For example, you can give users who must accomplish high-priority work more resources and better response time. To associate TSO/E users with different levels of performance, use SYS1.PARMLIB member IEAICSxx. For more information about SYS1.PARMLIB member IEAICSxx, see .

Although you cannot, through SYS1.PARMLIB member IEAICSxx, associate TSO/E commands with different levels of performance, you can provide different levels of performance for both commands and user-written exit routines, depending on where you place them. By default, most TSO/E commands reside in SYS1.CMDLIB, and exits IBM® provides reside in the same place as the load modules with which they are associated. You can install commands and exit routines in PLPA (pageable link pack area), in FLPA (fixed link pack area), in the LNKLST concatenation, or in a private STEPLIB data set.

Using PLPA or FLPA provides the best performance. The commands reside in virtual storage, so the system does not have to do the I/O required for retrieving commands from SYS1.CMDLIB. However, placing commands in PLPA or FLPA:

Uses more common storage.
Makes it more difficult to make changes. To update commands or exits in PLPA or FLPA, you must re-IPL your system.
Makes the process of installing TSO/E less straight-forward. When you install a new release of TSO/E, you must copy the new versions of the commands to PLPA.

You should move all reentrant TSO/E modules that can reside either above or below 16 MB in virtual storage to PLPA. If your system is storage-constrained, you may want to move just the most commonly-used commands and exit routines to PLPA. To identify the most commonly-used commands, use System Management Facilities (SMF). For more information about using SMF, see Monitoring TSO/E resources.

You may want to move commands that are infrequently used, but must provide good response time, to FLPA. For example, if users log on infrequently, you may want to page-fix the modules associated with the LOGON command. However, note that some of the modules associated with the LOGON command reside below 16 MB in virtual storage. Therefore, if your system is storage-constrained, you may not want to page-fix these modules. To page-fix modules associated with logon processing, update SYS1.PARMLIB member IEAFIXxx. For more information about IEAFIXxx, see .

Although the performance of commands and exit routines in the LNKLST concatenation is generally not as good as PLPA, modules are easier to update. To update modules, you must build a new copy of the LNKLST directory. For information about how to build a new copy of the LNKLST directory, see .

Note: If you move the following subcommands of the EDIT command from PLPA, do not delete them from the LNKLST concatenation: ALLOCATE, ATTRIB, EXEC, FREE, HELP, PROFILE, RUN, SEND, and SUBMIT.

You should avoid placing commands and programs in STEPLIB data sets, except when you are testing them. Using STEPLIB data sets could adversely affect the performance of your system because each time you execute a command or load a program, the system searches the STEPLIB data set before searching any others. If you must use STEPLIB data sets, you should not concatenate them. Response time is usually better if you use one large data set instead of concatenating several smaller data sets.