> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of Binyamin Dissen > Sent: Wednesday, May 30, 2007 11:20 AM > To: [email protected] > Subject: Re: Is there a cost in switching AMODEs? > > On Wed, 30 May 2007 09:45:04 -0700 Edward Jaffe > <[EMAIL PROTECTED]> > wrote: > > :>Binyamin Dissen wrote: > :>> Is there much of a cost to switching amodes? > > :>> Is it worth writing code to be able to run completely in 64 bit mode > (and > :>> maintain the top half of the registers) or is it fine to switch in and > out > :>> when referencing storage above the bar? > > :>> POPs does not indicate anything. > > :>In my experience, excessive switching of addressing mode is quite > :>expensive. I suspect it's because the entire pipeline must be flushed. > > I didn't see that in the POPs. > > -- > Binyamin Dissen <[EMAIL PROTECTED]>
A pipe-line flush is usually indicated quite clearly in the PoPs as a "checkpoint synchronization" operation. My PC routines usually set AMODE(64) quite early (after testing FLCARCH) and stay in AM64, unless a system service, like SETFRR, requires AM31. Saving and restoring AM64 is quite painless with the linkage stack (BAKR,PR) instructions. The LLGT, LLGTR instructions are quite useful for purifying "dirty" 31-bit pointers. If you already have "clean" 31-bit pointers, then using LA Rx,0 is an easy way to clear the entire 64-bit register before loading the full word pointer. This paradigm provides backward compatibility to older 31-bit machines. Using these techniques, my mainline PC routine code runs in AM64 or AM31 without much dual-pathing. Only the entry logic does some simple tests and cleans pointers. The remainder of the routine works correctly in either AM31 or AM64 without any further dual-pathing. Good luck. Jeffrey D. Smith Principal Product Architect Farsight Systems Corporation 700 KEN PRATT BLVD. #204-159 LONGMONT, CO 80501-6452 303-774-9381 direct 303-484-6170 FAX http://www.farsight-systems.com/ see my résumé at my website (yes, I am looking for employment) ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
