gtpi1m1rSystem Installation Support Reference

RCS I/O Queue Thresholding

User exit routine UCCTHR is provided as a default for processing a record cache subsystem (RCS) I/O queue threshold exceeded condition. This exit point, which is nondynamic, is invoked by entry point CJIVTTMR in control program CSECT CCRCSC whenever the I/O queue threshold value computed for an RCS subsystem is exceeded.

This user exit provides I/O queue depth statistics for a degraded record cache subsystem (RCS) controller on a periodic basis whenever a calculated threshold value is exceeded for the subsystem. System processing action depends on the action specified by the user exit in the thresholding parameter list provided.

An interface parameter list (IDSTHR) is provided by CJIVTTMR that passes relevant queue depth information. CJIVTTMR accepts the processing action that the user specifies in the parameter list on return.

General Conditions at Entry

The registers at entry to UCCTHR are:

R6
IDSTHR parameter list.

R11-R15
See User Exit Routines - Common Entry Conditions.

System Conditions at Entry

System state
Supervisor

System mask
Unmasked

Protect key
0

Address space
SVM.

Programming Considerations at Entry

  1. The parameter list IDSTHR is provided so the control program is the only code that is required to understand the internal system data structures. Because a menu of processing options is provided, you do not have to be aware of the internal data structures and, therefore, should not need to change them because of system changes.
  2. Return must be made to CJIVTTMR because that entry point restarts the periodic (1 second) timer interval for threshold monitoring.
  3. See User Exit Routines - Common Entry Conditions.
  4. See User Exit Routines - Common Programming Considerations for other considerations.

Programming Considerations on Return

  1. R14 will contain a return code, set by the user exit routine, that will show what action is to be taken. The following return code definitions are supported:
  2. See User Exit Routines - Common Return Conditions.

General Conditions on Return

See User Exit Routines - Common Return Conditions.