Examples of using REFPAT to define a reference pattern

To clarify the relationships between the UNITSIZE, UNITS, and GAP parameters, this information contains three examples of defining a reference pattern. So that you can compare the three examples with what the system does without information from REFPAT, the following REFPAT invocation approximates the system's normal paging operation:

REFPAT  INSTALL,PSTART=. . .,PEND=. . .,UNITSIZE=4096,GAP=0,UNITS=1

Example 1: The program processes an array in a consistently forward direction from one reference unit to the next. The processing of each element is fairly simple. The program runs during the peak hours and many programs compete for processor time and central storage. A reasonable value to choose for the number of bytes to be brought into central storage on a page fault might be 80000 bytes (around 20 pages). A logical grouping of bytes (the UNITSIZE parameter) is 4000 bytes. The following REFPAT macro communicates this pattern to the system:

REFPAT  INSTALL,PSTART=FIRSTB,PEND=LASTB,UNITSIZE=4000,GAP=0,UNITS=20

Example 2: The program performs the same process as in the first example, except the program references few elements on each page. The program runs during the night hours when contention for the processor and for central storage is light. In this case, a reasonable value to choose for the number of bytes to come into central storage on a page fault might be 200000 bytes (around 50 pages). UNITSIZE can be 4000 bytes and UNITS can be 500. The following REFPAT macro communicates this pattern:

REFPAT  INSTALL,PSTART=FIRSTB,PEND=LASTB,UNITSIZE=4000,GAP=0,UNITS=500

Example 3: The program references in a consistently forward direction through the same large array as in the second example. The pattern of reference includes a gap. The program references 8192 bytes, then skips the next 4096 bytes, references the next 8192 bytes, skips the next 4096 bytes, and so forth throughout the array. The program chooses to bring in data eight pages at a time. Because of the size of the gap and the placement of reference units and gaps on page boundaries, the system does not bring in the data in the gaps. The following illustration shows this reference pattern:

The following REFPAT macro reflects this reference pattern:

REFPAT  INSTALL,PSTART=FIRSTB,PEND=LASTB,UNITSIZE=8192,GAP=4096,UNITS=4