> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:IBM-MAIN@bama.ua.edu] On > Behalf Of Staller, Allan > Sent: Monday, June 13, 2011 9:41 AM > To: IBM-MAIN@bama.ua.edu > Subject: Re: When is performance really an issue? Was: Running an ISPF > applicction from one pds > > <snip> > " A CPU pipeline is the hardware advance that makes measuring program > CPU time a gambler's game, since there is no longer any guarantee at all > that a program will consume the same CPU time from one execution to the > next, even with totally identical inputs." > </snip> > > For a long as I can remember (IIRC MVT 21.7, long before pipelining), > there has been a statement in the SMF manual in the chapter dealing with > accounting similar to: > > "Measured CPU time is not guaranteed to be repeatable between 2 > successive executions of the same program and inputs" (my paraphrase).
Very possibly true, as I have never had the need nor the desire to even browse the SMF manual(s). OTOH it did used to be that two successive runs of the same batch program on the same mostly idle machine with exactly the same inputs would produce *nearly* identical CPU times (to the second, anyway). It was "close enough" for human use. Now such near-accuracy is just about impossible. I have seen differences of over 10% even on nearly idle machines. That's why I call it a gambler's game. Peter -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- 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
