On Fri, 7 Aug 2009 17:31:55 -0400 Bill Fairchild <[email protected]> wrote:
:>It certainly can't hurt to change the MVI/MVC to a single instruction: :> MVC 254(3,120),=120c' ' :>And, if possible, align the 120c' ' on at least a double word boundary. More precisely, the same doubleword alignment as the target field, i.e., if the target field is 3 bytes off of a doubleword the source field should be equally aligned. :>-----Original Message----- :>From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Farley, Peter x23353 :>Sent: Friday, August 07, 2009 2:50 PM :>To: [email protected] :>Subject: z10 and overlapping/destructive moves :>I am in the midst of a CPU optimization exercise for a COBOL program and :>ran across the following code sequence generated by the compiler: :> MVI 254(3),X'40' :> MVC 255(119,3),254(3) :>This code is generated in response to a simple COBOL "MOVE SPACES TO :>variable" instruction, where the variable is 120 bytes long. :>Did I or did I not see some discussion here or perhaps in a SHARE :>presentation that on a z10 machine overlapping/destructive moves wreck :>the pipeline and take *much* longer to execute as a result? Or am I :>imagining that? :>The reason I ask is that Strobe highlights this place in the code as a :>high-usage point, and I am struggling to understand why. :>TIA for any info you can provide. -- Binyamin Dissen <[email protected]> http://www.dissensoftware.com Director, Dissen Software, Bar & Grill - Israel Should you use the mailblocks package and expect a response from me, you should preauthorize the dissensoftware.com domain. I very rarely bother responding to challenge/response systems, especially those from irresponsible companies. ---------------------------------------------------------------------- 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
