> Question 1 > ========== > Does PR/SM dispatches an LPAR only when the number of physical > processors awaiting allows to dispatch all the logical processors > required for an LPAR simultaneously?
No. > For example suppose my machine has 3 physical CPUs, and with 3 lpars > defined as follows: > LPARA ? 3 logical processors > LPARB ? 2 logical processors > LPARC ? 2 logical processors > Option 1 ? Am I wasting a physical processor when LPARB or LPARC are > dispatched? > Option 2 - Or can the single physical processor left be dispatched > to serve another lpar? > If option 2 is the true one, are there spin-lock and loop related > problems if only a subset of CPUs is dispatched by PR/SM? Option 2, and yes, there can be cases where a dispatched logical processor can be spinning for a resource held by a logical processor which is not dispatched. z/OS detects this situation and informs LPAR. > Question 2 > ========== > Suppose that an LPAR running z/OS with 2 physical processors is dispatched. > The first physical processor completed its work. > The second physical processor is still burning cycles with for > example the CICS QR TCB > In other words, my z/OS at some moment got 2 physical CPUs but only > one TCB has really work to do. > Are both physical processors returned simultaneously to PR/SM or are > they returned independently to PR/SM as they become idle? > I mean, do the processors return one by one to the pool of available > physical processors or simultaneously on an LPAR base? Logical processors are dispatched and returned independently. > Question 3 > ========== > Suppose that I have 2 LPARs, one with weight 20 and the other with weight 80 > The one with weight 80 does not consume all its time slice and > returns the processor(s) to PR/SM > The one with weight 20 finds a way to use those cycles the other left ? > Now the LPAR with weight 80 wants more than its weight ? > Over which time interval are the weights averaged? Once a second? > Once a minute? Not averaged at all? LPAR calculates the share for each partition based on the weights of all of the active partitions. For a partition which is not in hiperdispatch mode, the share is distributed evenly among its logical processors. A logical processor which has not used its share is given some amount of dispatching preference over logical processors which have used more than their share. I don't know the time intervals over which the calculations are made. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
