Using GTF

For systems that are not part of a multisystem sysplex, using the generalized trace facility (GTF) can provide additional information. You can use GTF to monitor:

How frequently the RSA-message passes around the ring
The actual size of the RSA-message
The duration of the cycle time

To gather this information, trace the global resource serialization CTC channel program for a short period of time during peak processing. Place the following GTF trace options in a parmlib member that GTF reads when the trace is started:

TRACE=SSCHP,IOP,CCWP
IO=SSCH=(C44,C4C,C54)
CCW=(SI,DATA=8)
END

These sample statements trace the CTC links identified by device numbers C44, C4C, and C54. Replace these device numbers to trace the links that global resource serialization is using in your installation at the time of the trace. The data count (DATA=8) is small because the actual contents of the RSA-message are not of interest. The trace statements do record the number of bytes in the RSA-message; a length of 39 bytes indicates an empty RSA-message (an RSA-message that contains no resource requests).

If the RSA-message is almost always empty, you can probably set a higher RESMIL value without affecting response time. If the RSA-message is frequently close to full (more than 25K when the maximum size is 32K), set a lower RESMIL value to send the RSA-message around the ring more frequently. If the RSA-message is full even occasionally (more than five percent of the time), it is probably having an adverse effect on response time. Set a lower RESMIL value to send the RSA-message around the ring more frequently.

For more information about using GTF, see z/OS MVS Diagnosis: Tools and Service Aids and z/OS MVS Initialization and Tuning Reference.

When you examine the data, using either the GTFTRACE function of IPCS (interactive problem control system) or your own post-processing program, be aware that the direction (clockwise or counter clockwise) of the RSA-message is determined dynamically when the systems build the ring. Thus, an address used to send the RSA-message at one time might receive it at another time. Once determined, the direction of the message cannot change unless a system enters or leaves the ring.