> -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:ibm-m...@bama.ua.edu] On Behalf Of Supra Uche > Sent: Thursday, August 12, 2010 1:10 AM > To: IBM-MAIN@bama.ua.edu > Subject: Basic question about CPU instructions > > Hello List, > I want to learn how a cpu type change effects my application > performance. > When a new generation mainframe is produced, it comes with > hundreds of > new instructions. I think that new instructions run > applications more efficiently > than the previous ones. Also for example if i had a 1000 MIPS > capacity 1 CPU > old machine, the new generation mainframe comes with 1200 > MIPS capacity > per CPU. If I think like, "the number of mips increased also > the instructions will > be more efficient than the previous ones. So my total gain is > bigger than the > mips capacity increase", is that idea correct or not ? Or is > that directly related > with the operating system version? If i dont upgrade my z/OS, > will i able to > get the benefit of new instructions? > I hope i could explain myself. > Thank you.
New instructions do not necessarily run more efficiently than previous instructions. It depends on what the instructions do, of course. I have not tested it myself, but I've been told that on some processors, the MVCL instruction is actually slower than doing a corresponding loop using MVC. And I wonder if MVCLE is more efficient than MVCL. I also remember when IBM went from BiPolar machines (3090?) to CMOS (?). The packed decimal instructions performed dismally. Now, some of the recent z10 and above sure sound like they are more efficient. Such as using the new compare and branch instructions instead of the separate compare & branch instructions. But not always. If you need a "two way" compare, then "compare and branch" makes sense. But if you need a "three way" compare (such as compare against zero, branch one place if negative, another place if zero, and next instruction if positive), then a separate compare followed by 2 branch instructions might be more efficient than two "compare and branch" instructions. But without a z10 to test on, I don't know that for certain. Now, the OS level you're running has nothing to do with or influence the efficiency of the instructions in your program. So if you get a z10 or z196 and start using the new instructions, then you get the benefits of the new instructions. If an old instruction has its execution improved, then you get that improvement in your code. If an old instruction executes slower on the new processor, then your code will suffer. I think your general question has an answer of "false". Basically the new CPU is "faster" because of a better cycle time and because more efficient hardware or millicode. The two together are use to calculate the "MIPS" of the machine. Of course MIPS and even MSUs are now only marketting propoganda with little technical meaning. -- John McKown Systems Engineer IV IT Administrative Services Group HealthMarkets(r) 9151 Boulevard 26 * N. Richland Hills * TX 76010 (817) 255-3225 phone * (817)-691-6183 cell john.mck...@healthmarkets.com * www.HealthMarkets.com Confidentiality Notice: This e-mail message may contain confidential or proprietary information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. HealthMarkets(r) is the brand name for products underwritten and issued by the insurance subsidiaries of HealthMarkets, Inc. -The Chesapeake Life Insurance Company(r), Mid-West National Life Insurance Company of TennesseeSM and The MEGA Life and Health Insurance Company.SM ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
