The load balancing of activity between I-streams and ECBs during CRUISE RESTORE tape roll-in needs to be improved

The load balancing of activity between I-streams during the tape roll-in phase of a restore is not very effective. If the default DEFRC option is setup, most of the processor MIPS are used up by the driver ECB doing “DEFRC”. A ZSTAT U display will show the I-stream where the driver ECB is running as almost fully utilized. The other I-streams are far less busy and show very poor utilization. The APAR PM PM48151 does provide an option to replace DEFRC with EVNTC processing. However, this solution is not easily optimized and is difficult to maintain.

It is not easy to determine, what the appropriate settings for the values in i_cruusr.h need to be. It requires a trial and error process. Once some settings have been arrived at they are good only for the current configuration. If the environment changes, e.g. new DASD, new CPU or change in restore mix, those values have to be readjusted and tuned again. This is at best cumbersome. Another limitation is that those settings are global and apply across all tables. What might work best for one table or function, may not work as well for another. These values should be configurable at run-time through the table parameters. Suitable default values can be provided in the default settings so these do not need to be coded for each and every table in every case.
Another consideration relates to the distribution of work between ECBs. Currently the existing ECB reads the tape blocks, then CREMS a new ECB for the next tape read, and then continues processes the current data by copying to pool and updating the cross-reference table. This process is repeated as the each ECB either reads from the tape or processes the data block read by a previous ECB. Perhaps a different distribution or dispatching scheme could improve performance. One option is to reverse the roles and allow the primary ECB to do the tape reading, while the created ECB do the file updates. Another option is to flip-flop the role for each iteration, so the work of the ECBs alternates between reading tape blocks and filing the data blocks and updating the cross-reference files.