In most cases, the z/OS operating system dispatcher provides optimum performance. However, if your application makes extensive use of ICSF functions, you should consider using one or both of these:

• CCF Systems Only: If your application runs in SRB mode, use the SCHEDULE macro or IEAAFFN callable service. You should consider scheduling an SRB to run on a processor with the cryptographic feature installed (using the FEATURE=CRYPTO keyword on the SCHEDULE macro). For more information on the SCHEDULE macro, refer to z/OS MVS Programming: Authorized Assembler Services Reference LLA-SDU.

  Restriction: The FEATURE=CRYPTO keyword should not be specified when running on an IBM zSeries 990.

• Use the IEAAFFN callable service (processor affinity) to avoid system overhead in selecting which processor your program (specifically, a particular TCB in the application) runs in. Note that you do not have to use the IEAAFFN service to ensure that the system runs a program on a processor with a cryptographic feature; the system ensures that automatically. However, you can avoid some of the system overhead involved in the selection process by using the IEAAFFN service, thus improving the program’s performance. For more information on using the IEAAFFN callable service, refer to z/OS MVS Programming: Callable Services for High-Level Languages.

IBM recommends that you run applications first without using these options. Consider these options when you are tuning your application for performance. Use these options only if they improve the performance of your application.