Performance considerations

Follow the guidelines found in the z/OS MVS Initialization and Tuning Reference. If your installation is running Workload Manager, follow the guidelines found in z/OS MVS Planning: Workload Management.

VTAM®, TCP/IP, and some associated server applications must be able to obtain cycles to maintain their network presence. The following dispatching priority guidelines apply for these functions:

In general, you should set VTAM and TCP/IP to a higher dispatching priority than that of the applications that use their services.
For server applications such as OMPROUTE, TN3270E Telnet server, IKED, NSSD, and FTPD, set the priority value to the same value to which TCP/IP is set, or to a priority that is just below that value. If you are using WLM, assign these tasks to the SYSSTC service class. Additionally, you can make these tasks non-swappable so they are available during periods of high CPU usage. The MVS™ default program property table sets Telnet to be non-swappable and privileged, which automatically assigns the task to the SYSSTC service class.
Set non-critical applications, such as Policy Agent and TRMD, to a lower priority.
Set the SNMP agent and all the SNMP subagents to the same WLM service class so that they all have the same dispatching priority. Timeouts can occur if the SNMP subagents are set to a lower dispatching priority than the SNMP agent.

On systems with significant FTP activity, you can improve performance by placing the FTP program objects into the dynamic link pack area (LPA). Putting the FTP program objects into the dynamic LPA eliminates the need to load these program objects from DASD for each FTP session. You can place these program objects into the dynamic LPA using either of the following methods:

Include the following statement in the PROGxx member of SYS1.PARMLIB and then issue a SET PROG=xx command:
```
LPA,ADD,MODNAME(EZAFTPLS,FTPDNS,EZAFTPLC,FTP),DSNAME(LNKLST)
```

Issue the following SETPROG command:

SETPROG LPA,ADD,MODNAME(EZAFTPLS,FTPDNS,EZAFTPLC,FTP),DSNAME(LNKLST)

Tip: You can also place the SET PROG=xx command or the SETPROG command in a COMMNDxx SYS1.PARMLIB member to have the command issued at IPL time.

Requirement: If maintenance is applied to these program objects, you must update the program objects in storage using one of the following methods:

Issue an LLA refresh command, and then issue a SET PROG=xx command that points to a PROGxx member that contains the following command:
```
LPA,ADD,MODNAME(EZAFTPLS,FTPDNS,EZAFTPLC,FTP),DSNAME(LNKLST)
```
Issue an LLA refresh command, and then issue the following SETPROG command:
```
SETPROG LPA,ADD,MODNAME(EZAFTPLS,FTPDNS,EZAFTPLC,FTP),DSNAME(LNKLST)
```

For more information, see z/OS MVS System Commands.