Isn't "fall back to the CP" because one would typically want one's work to run *somewhere* even if a zIIP were not available but perhaps a CP was?
zIIP's are all about software costs, right? So scheduling work is like buying a seat on Southwest. I need to get there, so if none of the "wanna get away" seats are available, I will buy a full-fare seat. Charles -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Phil Smith Sent: Thursday, June 7, 2018 8:38 AM To: [email protected] Subject: Re: Why are highly busy zIIPs worse than highly busy CPs? Peter Hunkeler wrote, in part: >There are some statements around zIIP utilization which I read here and there. Statements like: >- "You should not utilize one zIIP more than 30%, two zIIPs more than 60%..." >- "A task may become delayed for up to 3.2 ms (actually ZIIPAWMT) before the busy zIIP asks for help from a CP". There are some knobs that can control this. And it's surely YMMV. If you had, for example, one heavyweight thread that was zIIP-eligible, one might assume that it could saturate that zIIP without issues. But that's not going to be a common scenario. Scheduling an SRB isn't cheap. I don't know whether that's why, but for whatever reason, IBM has built this "fall back to the CP" mechanism. Kathy Walsh of IBM has a pretty good session that talks about this; I saw it at the IBM Systems Technical University in Orlando last month. Session is z101268.pdf; I can't find it on the web, either under that number or by searching some key strings in it. Sorry... -- ...phsiii Phil Smith III Senior Architect & Product Manager, Mainframe & Enterprise Distinguished Technologist Micro Focus (Voltage) [email protected] T 703-476-4511 M 703-568-6662 Herndon, VA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
