Hi, There does not seem to be any decent documentation on the workings of the z/os Dispatcher.
>From Some Old Documentation I have in my MVS/XA or MVS/ESA days I have the >following: ------------------------------------------------------------------------------------- >snip MVS maintains two units of work represented by a Task Control Block (TCB) or a Service Request Block (SRB). TCBs are created as a result of a ATTACH Macro. SRBs are created as a result of SCHEDULE macro. The MVS Dispatcher maintains a queue of Address Spaces (ASIDs) which are in the system. The queue is sequenced in dispatching order - the highest priority and next to get control of the CPU is on the top. The dispatcher selects SRBs and TCBs to be executed. The selected unit of work (SRB or TCB) will control the processor until: a) a task enters a wait -or- b) an interrupt occurs (I/O, Machine Check, Program, SVC, or External) If there are no tasks ready to execute, than the dispatcher loads the registers and environment of IEEVWAIT with a WAIT PSW with all zeros. When The Dispatcher Gets Control: 1)The Global Dispatcher selects Global SRBs for dispatch. The operation is serialized so that it executes only on a single processor at any one time. 2)The Global Dispatcher first examines the presence of special exits. 3)The Global Dispatcher next dispatches Global SRBs in the order that they are queued. 4)The Global Dispatcher next activates the highest priority ready address space on an available processor. 5)The ASCB True Ready Queue contains ASCBs for address spaces that are immediately dispatchable. The ASCBs on The True Ready Queue are sorted in dispatching priority order, so that the Dispatcher merely selects the ASCB that is at the head of the queue. 6)The True Ready Queue is not maintained by the Dispatcher but by SRM (System Resource Manager) which, adjusts address space dispatching priorities and initiates swapping operations. 7)After this point the Local Dispatcher can execute in the address space. 8)The Global Dispatcher has activated an address space on a processor, it transfers control to the Local Dispatcher which runs "in" that address space. 9)The Local Dispatcher first examines the queue of Local SRBs anchored in the ASCB field (ASCBSPL). If any SRB holds the local lock, that SRB is dispatched first. The dispatcher then dispatches the SRBs in the order they are queued. 10)After the Local Dispatcher has processed the Local SRBs, it examines the Interrupt Queue Element Block (IQEs) from the Address Space Extension Block (ASXB). 11)The Local Dispatcher examines each IQE and chains the IRB onto the Request Block (RB) Queue for the TCB where it will execute. 12)The Local Dispatcher then examines the queue of TCBs anchored to the ASXB field ASXBFCTB. If any TCB holds the Local Lock for the address space, the dispatcher selects it first. If the Local Lock is not held, the Dispatcher selects the TCB that has the highest priority. 13)Once the Dispatcher selects a TCB, it activates the program described by the first Request Block (RB) on that TCBs RB Queue. The RB could be a Program Request Block (PRB) that describes a link; an SVC Request Block (SVRB) that describes a type 2,3, or 4 SVC routine, or an IRB (Interrupt Request Block). snip ------------------------------------------------------------------------------------------- My Questions Are: A) With respective to the above description of the Dispatcher. Are the statements still viable for Z/OS ? B) Where can I find IBM documentation on the Z/OS Dispatcher ? How does it Work ? C) Does Work Load Manager complement or replace the z/OS Dispatcher ? Thanks For Any Information Paul D'Angelo ____________________________________________________________ Click here to find the perfect banking opportunity! http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTMLunqQ0McnxuhXCRETqvqRT2FxzuYaqOFcVE880id8z7r0pNk8Qg/ ---------------------------------------------------------------------- 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
