Ted, Isn't the statement " I'm pretty sure it's derived from the equation 128 mics * 6500 = 8.32 ms" a little arse about? That's how service units are derived, but Connect time and EXCP counts are not derived, they are recorded.
And connect time is definitely not constant. With FICON the attribution of connect time varies from vendor to vendor, and transfer time varies with path activity such that connect time can be double accounted. I'd go as far as to say that in going from ESCON to FICON connect time became one of the more unreliable IO metrics. I still use connect time for some things, but I agree with Bill that IO service units derived from Connect Time are somewhat useless. I think you should restate what you are disputing, or show me which EXCP count field is recorded incorrectly when IOSERV=TIME is used. EXCP counts are EXCP counts. Connect Time is Connect Time. The only thing that IOSERV changes is whether IO services units are derived from EXCP counts or Connect Time. If for some reason you ignored block count fields and created a block count from IO service units then that result would change, but who would do that in the first place? Finally, my Guru has spoken! I recalled that Barry calculated both EXCP and IOTM from Service Units in the MXG Type72 record, and while checking that I found this interesting note: /* NOTE: PRIOR TO MVS/ESA 5.2, IO SERVICE UNITS COULD BE BASED ON */ /* EITHER EXCP COUNT OR IO CONNECT TIME, AND MXG CALCULATED TWO */ /* VARIABLES, PGPEXCP AND PGPIOTM TO GIVE THE RAW IO UNITS. AS */ /* THERE WAS NO FLAG IN TYPE72 TO IDENTIFY WHICH UNITS WERE USED, */ /* BOTH VARIABLES WERE CALCULATED KNOWING ONLY ONE WAS VALID. */ /* WHEN DEVICE CONNECT TIME WAS USED FOR SERVICE UNITS, A SERVICE */ /* UNIT WAS DEFINED AS 65 CONNECT TIME UNITS, AND A CONNECT TIME */ /* UNIT IS 128 MICROSECONDS, HENCE THE 8320E-6 FACTOR IN PGPIOTM. */ /* BUT BEGINNING WITH MVS/ESA 5.2, IO SERVICE UNITS CAN ONLY BE */ /* BASED ON EXCP COUNT, SO PGPIOTM IS FORCED MISSING FOR 5.2+. */ So based on that it would seem that IOSERV=TIME is no longer honoured and IO Service Units are always based on EXCP count. It also corrects my 6500* 128 calculation - it should be 65. Ron Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of > Ted MacNEIL > Sent: Friday, August 14, 2009 7:12 AM > To: [email protected] > Subject: Re: [IBM-MAIN] Degraded I/O performance in 1.10? > > >If I were doing I/O performance measurement and tuning today, I would most > definitely not use that number. > > Why not? > That is what it is -- constant. > I'm pretty sure it's derived from the equation 128 mics * 6500 = 8.32 ms. > > >Since you are using the number, you should verify its accuracy and, if not > accurate any more, ask IBM yourself or else find a more modern analysis of > average I/O service time. > > The number is good for the 'quick and dirty'. > I never said that Ron's suggestion for the analysis of I/O from RMF (etc) was > wrong. > Nor did I say I was using the number, myself. > I was just disputing the comment that EXCP's were only block counts. > That depends on the setting (TIME or COUNT). > And, I believe COUNT is still the default. > - > Too busy driving to stop for gas! > ---------------------------------------------------------------------- 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
