> I just wanted to sound people out about converting a dataspace to a common > area above the bar. The main interest is the effect it would have on CPU > usage. > > To put it into context, the dataspace is used for a set of tables which are > used by the application programs. There are around eight thousand tables > currently occupying about a gigabyte of virtual storage. This is a large > installation with excess of 700 million transactions per month plus a heavy > batch load. The application programs make extensive use of these tables. > > Whenever an application program needs an element of one of the tables it > calls a standard assembler module which uses access register mode to search > the table in the dataspace and then returns the requested element to the > application program. > > If the set of tables were placed above the bar then access register mode > would not be needed as the tables would be directly addressable in 64 bit > addressing mode. > > It all seems much simpler so, at first sight, it would be expected to use > less CPU. A reduction in CPU would be the main justification for doing the > conversion.
As long as there is no ALB miss, the hardware performance for a data space storage access is no different than for non-data space. Converting from data space to memory object would save you the instructions for setting ARs, and possibly AGIs if the setting of an AR is too close to the use of the AR in address generation, and possibly an ALB miss each time your routine is called. Since the ALB miss may result in cache misses during ART, that is probably the most significant effect. However, all of that is probably next to nothing compared to the cache misses when you access the tables, and that will not be affected by data space vs. memory object. HIS sampler data (available on z10 and newer machines) is the best way to determine how much time you are spending in this code. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
