Purpose
Displays cell availability and usage information generated by the TDP internal memory management system. The information is accumulated from the time the current TDP was started; there is no command to reset it.
Syntax
where:
- VERIFY
- Specification that the actual number of z/OS PC cells that are currently in use is to be displayed.
Usage Notes
When TDP is started, the following number of each cell size is obtained.
| Cell Size | Number of Cells |
|---|---|
| 64 bytes | 500 |
| 128 bytes | 500 |
| 240 bytes | 150 |
| 256 bytes | 500 |
| 352 bytes | 500 |
| 416 bytes | 500 |
| 992 bytes | 500 |
When IACMODE PC is specified, the following number of each XMS cell size is obtained.
| Cell Size | Number of Cells |
|---|---|
| 256 bytes | 200 |
| 416 bytes | 200 |
| 992 bytes | 390 |
Each time TDP is started, the number of cells can be increased using the TDP ADD CELLS, ADD XMSCELLS, and INITIAL IOBUFS commands in the TDPPARM dataset. While TDP is running the number of cells can be increased using the TDP ADD CELLS and ADD XMSCELLS commands. There is no way to reduce the number of cells.
When you execute the DISPLAY CELLS command, TDP displays the following information about cells in the memory management system:
| Column | Description |
|---|---|
| CELSZ | Size, in bytes, of a cell. |
| AVAIL | Number of cells not currently in use. |
| INUSE | Number of cells currently in use. |
| MXUSE | Maximum number of cells used at any one time. This will include any cells reserved for IOMODE PC interface usage. |
| GMAIN | Number of times a cell was dynamically obtained. Normally, if no cell is available the TDP process will be suspended until a cell is made available, but under certain circumstances a cell will be dynamically obtained to satisfy the request. A cell dynamically obtained is freed when no longer in use. PC cells are never dynamically obtained. Overall throughput can be impacted since dynamically obtaining a cell is less efficient that reusing an available cell. The larger the number of dynamic actions, the greater the potential performance impact. |
| PC | Number of cells reserved for use by the IOMODE PC interface at any one time. |
| #WAITS | Number of times a TDP process was suspended because no cells were available. Normally, if no cell is available the TDP process will be suspended until a cell becomes available. Overall throughput can be impacted since a suspended TDP process is not available to process other work. The larger the number of suspensions, the greater the potential performance impact |
If INITIAL IACMODE PC is specified, information about cross-memory cell shortages is also displayed. That information could be:
- TDP1250, which indicates the number of times that at least one of the three cross-memory cell pools was exhausted. Each request requires one cell from each of the three cross-memory cell sizes. If any of the sizes is unavailable, the request must wait.
- TDP1251, which indicates the number of times that no cell was available to process a request that required more than one cell from the largest cross-memory cell pool
Except for a small number of cells used for specialized purposes, all cells are allocated from 31bit storage
If all available cells of a given size are used at one time, the following message is issued:
TDP0021 **WARNING** 100% of <size> BYTE CELLS IN USESuch a message appears at most once for each cell size.
Example: DISPLAY CELLS
D CEL
Completion Message
The result of the DISPLAY CELLS command is in the following format:
TDP0501 CELSZ AVAIL INUSE MXUSE GMAIN PC #WAITS TDP0528 00064 00498 00002 00042 0000000 00000 00000 TDP0528 00128 00496 00004 00006 0000000 00000 00000 TDP0528 00240 00499 00001 00043 0000000 00000 00000 TDP0528 00256 00491 00209 00247 0000000 00200 00000 TDP0528 00352 00497 00006 00006 0000000 00000 00000 TDP0528 00416 00497 00203 00204 0000000 00390 00000 TDP0528 00480 00005 00001 00005 0000000 00000 00000 TDP0528 00992 00498 00392 00890 0000000 00390 5265* TDP0528 12272 00004 00002 00006 0000000 00000 12272* TDP0529 OVERSIZE CELLS, INUSE: 1 MAXUSE: 0 GETMAINS: 1 TDP1250 WAITS FOR INITIAL PC CELLS: 0 TDP1251 WAITS FOR ADDITIONAL PC CELLS: 0 TDP0500 ADDITIONAL I/O CONTROL BLOCKS OBTAINED: 0
Notes on the Example
TDP1250 and TDP1251 appear only if IACMODE PC is specified.
TDP0500 appears only if TEST is enabled, IOMODE IOSDRIVR is specified, and CIC-type CPs are being used. Note that the I/O Control Blocks mentioned are not IOBUFS.
The #WAITS entry that contains an asterisk to the right of the five-digit number (00001*) indicates that TDP is currently waiting for the 12,272 byte cell size.
The #WAITS entry that contains an asterisk in the last position of the five-digit number (5625*) indicates that the #WAITS counter has wrapped (that is, it is a very large number).