David, I believe that the 2:1 ratio can be pretty well dead and buried, especially with enhancements like Hyperdispatch.
There were two affects as I recall. One was that the excess number of LP increased CPU time through increased HSB miss, and that low weight LPARs with way too many engines would steal capacity because of the LP timeslice. Back in CMOS days I found that the 2:1 rule was almost always beneficial, but nowadays on a z9-408 we run in excess of 10-15 LPARS with at least 2xLP each sharing 4 or 6 PP and there is no noticeable problem. We run test loads from time to time moving some LPARS between shared and dedicated PP so I expect a significant difference would have been noticed. Of course YMMV, especially if you are running extreme ratios (e.g. a z196-715 with ten LPARs of 15xLP each). Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of > Mark Zelden > Sent: Tuesday, August 24, 2010 9:11 AM > To: IBM-MAIN@bama.ua.edu > Subject: Re: [IBM-MAIN] LP:PP ratio? > > On Tue, 24 Aug 2010 11:21:46 -0400, O'Brien, David W. (NIH/CIT) [C] > <obrie...@mail.nih.gov> wrote: > > >Has the recommended ratio for Logical to Physical processor changed in the > last 10 years or so? > > > >There was a time where a ratio above 2:1 led to something called Short > Engine Syndrome or generally sluggish CPU performance. > > > >A colleague in the office now maintains the WSC has changed the acceptable > ratio to 3:1, which just happens to be where we are. > > > >If someone could point me to a definitive IBM statement, I'd appreciate it. > > > > Since it is just an "ROT", there won't be any definitive statement. What > matters is if YOU (your shop) can live with the overhead. > > Search the archives, this has been discussed a number of times. > > The last time I posted about this was October 11th 2007. Search Google > groups or the archives for "Logical to Physical CPU ratio ROT". > > -- > Mark Zelden - Zelden Consulting Services - z/OS, OS/390 and MVS > mailto:mzel...@flash.net > Mark's MVS Utilities: http://home.flash.net/~mzelden/mvsutil.html > Systems Programming expert at http://expertanswercenter.techtarget.com/ > > ---------------------------------------------------------------------- > 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 ---------------------------------------------------------------------- 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
