We've had zIIPs for years. We monitored usage but were never terribly concerned as long as numbers didn't skyrocket. When we moved to DB2 V10, however, we were warned that 'some customers' were experiencing serious performance problems when zIIP eligible work spilled over to general CPs. The reason, we were told, was that while general CP management had evolved over the decades with a huge boatload of OS code to handle contention, zIIPs were newcomers that were more or less on their own in playground competition. The wiry little guys with little bully protection.
The message we got was that an overloaded zIIP could lead to performance problems--and rolling average spikes--that could be worse (!) than having no zIIP at all. We were sufficiently alarmed that we were moved to buy yet another zIIP to guard against calamity in production. Because we acquired the extra zIIP early on, I can't say what the consequence would have been if we had done nothing, but this is certainly the tale I'd rather be telling. . . J.O.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 323-715-0595 Mobile 626-543-6132 Office ⇐=== NEW [email protected] -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Peter Hunkeler Sent: Thursday, June 07, 2018 9:21 AM To: [email protected] Subject: (External):AW: Re: Why are highly busy zIIPs worse than highly busy CPs? >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? If you meant no zIIPs are available to the LPAR (not configured or the CEC does not have some), then there is no fall-back. Work units get queue on CP work queues initially; the zIIP work queue is not being used. At least this is how I understand it. If you meant no free zIIP capacity is available, then part of the decision might have been that initially you could have only half as many zIIPs as you had CPs. -- Peter Hunkeler ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
