IBM Mainframe Discussion List <IBM-MAIN@BAMA.UA.EDU> wrote on 06/13/2007
12:37:38 PM: > Ordinarily, as PR/SM dispatches CPs to LPARs, a Logical CP may have a > task dispatched to it, but beneath it, it has no physical CP. > Milliseconds later, the CP may well be back and the task actually runs. > But when we had our 2064-104 and it's cap kicked in, the CP was gone for > awhile, not for a few seconds at a time but for minutes, and response > time suffered noticeably. It seems that, with fewer engines, and a > steeper climb to exceed the cap, an engine may be gone for quite awhile, > compared to a several-engine system whose cap is closer to machine > capacity. It was also being capped during lunch time, when customarily > our usage dropped anyway, so we did not logically need that 4th CP. But > the distinct impression we got was that MVS was not aware that one LCP > had become only a phantom, and MVS had not varied a CP offline, but > instead continued to attempt to dispatch work to it. > > 1. Given that an over-busy LPAR looses one or more CPs from being > dispatched for more than milliseconds, does MVS know that the CP is > gone? (Currently we have a 2094-S08.) As the MVS scheduler dispatches, > does a 4-engine LPAR's MVS treat the situation internally as if it still > had 4 engines, while one of them is out-to-lunch due to capping, or is > MVS instead informed, varies the CP offline internally, and dispatches > its work on just the remaining 3 CPs? It would seem that, if the > situation has become significant enough for an engine to be offline long > enough (minutes to an hour) but without MVS's knowledge, then it might > be more beneficial if (perhaps by automation) an engine was officially > varied offline, allowing work that is dispatched to actually run, rather > than having the TCB imagine that it is going to run on a LCP whose PCP > is not there anymore. Of course the follow-up question wonders whether > the now-3-CP environment will have one of its PCPs taken away as PR/SM > figures that it has to actually pinch somewhere to fix its average? > Observations? And how has the group-of-capped-LPARs worked? LPAR dispatching does not work the way you are suggesting. LPAR spreads a zone's share equally among the online Logical CPs in the zone. You may see a Logical CP getting dispatched only once every 500 milliseconds, but that is because MVS has it in a wait due to Alternate Wait Management. If the Wait bit is not on in the PSW, a Logical CP gets an equal share of the zone's share. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY -----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Jim Mulder Sent: Wednesday, June 13, 2007 2:30 PM To: IBM-MAIN@BAMA.UA.EDU Subject: Re: PR/SM -- WLM Capping Jim: Thanks for the information. But always eager for deeper insights, is there a manual or Redbook that explores this a bit further? Thanks, Rick Confidentiality Notice: This email is intended for the sole use of the intended recipient(s) and may contain confidential, proprietary or privileged information. If you are not the intended recipient, you are notified that any use, review, dissemination, copying or action taken based on this message or its attachments, if any, is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy or delete all copies of the original message and any attachments. Thank you. ---------------------------------------------------------------------- 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
