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SVC 018

SVC 018 is a Type 2 SVC  invoked by the BLDL/FIND macro to obtain a directory entry for a module to be loaded. This macro does not get a lock.

BLDL/FIND searches specified load libraries for a module or list of modules. It usually searches the STEPLIB, JOBLIB, and link list libraries until it finds the module.

Hints

If a load module is not found in the first library, another library will be searched. This can result in high CPU use to SVC 018 on the CPU Use by Program report, high wait in STEPLIB or JOBLIB on the Resource Demand Distribution report, and high activity to specific cylinders on the I/O Facility Usage report.

To improve performance, either reduce the number of module searches or reduce the number of libraries that must be searched. Because most module searches are done for module loads, reducing the loads will reduce the searches. See the SVC 008 performance hint for information about reducing loads. To reduce the number of libraries searched, make sure the minimum number of libraries are concatenated to STEPLIB and JOBLIB. In some cases, users have completely eliminated STEPLIB and JOBLIB, by loading all modules from the link list.

In an IMS region, modules can be preloaded. If a module is not preloaded, a significant amount of CPU will be attributed to SVC 018.

In a CICS region, the first time a module is referenced after a newcopy, a BLDL is done.

Reference Sources

IBM z/OS MVS Diagnosis Reference

IBM z/OS DFSMSdfp Advanced Services

IBM z/OS DFSMS Using Data Sets

IBM z/OS DFSMS Macro Instructions for Data Sets