It's really not more complicated. Higher priority work always gets the computing cycles it needs, except as it relates to competition at the same or higher priorities. Low priority cannot contribute any resources, since it doesn't have anything that higher priority work needs.
In other words, work that is a dispatching priority (DP) of 255 has no higher level competitors and therefore will only experience delays as it relates to those that are also at DP 255. If a unit of work is at DP 240, it cannot interfere, except in the small instance of where it may have gained control and is allowed to finish out its dispatch cycle before being interrupted. One of the problems is that people presume that CPU utilization reflects the overall state of the system for all units of work, which it doesn't. CPU utilization reflects the probability that the CPU will be busy servicing someone else when a task becomes ready. Therefore higher priority tasks "see" a completely different utilization [i.e. probability] than low priority tasks. If you're experiencing a problem, then it is probably related to your higher priority work meeting its goals and therefore not requiring anything more based on your WLM definitions. Another problem is that your higher priority work could be defined with "impossible" goals and therefore ends up being ignored. Both of those cases will result in your higher priority not getting any help if usage goes up. Adam -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Natasa Savinc Sent: Tuesday, February 19, 2013 2:54 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Low priority workload Hello! >From time to time (certain days in a month) we hit group or system limit. We >have different types of workload defined in WLM. Among others, most batch jobs >have the lowest priority. At the peek times they apparently get no CPU >resources, but when we make report at the end of the day, they managed to get >some CPU seconds. We would prefer that those seconds were allocated to >important online transaction. There are two opinions amoung our sysprogs: one is that we should cancel all low priority workload in order to help our online get all the resources, the other is that that is not necessary, as batch isn't getting any online's CPU resources anyway. It seams that when you hit the limits things become more complicated. Any thoughts about our dilemma? Any experiences with life on the edge? Regards, Natasa ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
