On Mon, Jan 20, 2014 at 3:38 AM, John Blythe Reid <[email protected]>wrote:
> Hello, > > 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. > > I would be very interested on anyone's opinion on this subject. > > Regards, > John. > > > That's an interesting question. And it triggered some more questions in my mind. First, is your entire application written in AMODE(64)? If not, doesn't that means that your assembler routine would be switching AMODEs to/from AMODE(64) and the caller's AMODE on each call? Do you cache the ALET for your data space somewhere easy to retrieve? What about the 64 bit address of the AMODE(64) table? It is cached somewhere? Or, in either case, does the caller supply the address/ALET to the assember routine. I guess the main question that occurs to me is: "How much difference is there between doing two SAC instructions (to change the enable/disable dual address mode) between doing a BASSM and BSM (to change AMODEs)?" I also wonder if there is any difference in speed in fetching some data from a Data Space versus the home address space? -- Wasn't there something about a PASCAL programmer knowing the value of everything and the Wirth of nothing? Maranatha! <>< John McKown ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
