SIIS instruction on a Z14.

Products

• Disk Backup and Restore - MVS
• DISK BACKUP AND RESTORE- ADD-ON OPTIO
• DISK BACKUP AND RESTORE

Issue/Introduction

Code optimization for SIIS instruction on a Z14. 

Environment

Release : Disk Backup and Restore 12.5

Cause

The EDF data with the new version of the CP3EXTR utility produces report that does have the SIIS violations in ADSMI002. In the doc we've seen so far (Strobe reports and HIS data), the other top CPU consumers were just heavy-hitter modules and didn't have any SIIS problems in the sections of code that the tools were reporting on.

 

The SIISP vector that's now in the report is extremely helpful. It does show that the SIIS percentage is showing up when the job starts. The vector that is in the EDF output shows a SIIS % of 4.2% as the highest SIIS percentage from any of the reporting intervals, and this interval was when the job started. For the 5-minute interval, the job started 3 minutes into that interval.

Resolution

Investigate a Strobe analysis on Disk archiving/backup jobs to determine the below offset length for each.

ADSDB001 ( at offset 2c0 length 64) , KWIKSHR4 ( at offset 100 length 64),  ADSMI0002 (at offset 80 length 64), ADSUT042 ( at offset 280 length 64) and GSMFSCRN  ( at offset 500 length 64)  are programs who have the more CPU impact.

Apply the PTF SO15101 for code optimization for SIIS.

Additional Information

Refer to the IBM documentation Identifying “Store Into Instruction Stream” (SIIS) Inefficiency by Using CPU MF Counters to understand the problem.