Deadline Scheduling

Deadline scheduling is a technique that allows a user to schedule a job by time-of-day, week, month, or year. The job's priority remains in force, but as the deadline approaches, JES3 increases the job's priority. Thus, deadline scheduling increases the likelihood that the job will be scheduled for execution by the specified deadline.

Note: As a result of deadline scheduling, a job will be reclassified when its priority is changed. Depending on the priority that is used in your installation's classification rules in the WLM policy, this may or may not cause a new service class to be assigned to the job Changing the priority as a result of deadline scheduling does not affect when a job in a WLM-managed group is selected to run. Jobs waiting to be selected for execution by an WLM initiator are ordered by main service arrival time and not priority.

A deadline scheduling algorithm specifies how often and by what amount JES3 is to increase the job's priority. You must specify the algorithm on a DEADLINE initialization statement. You can specify a maximum of 36 deadline scheduling algorithms.

To specify deadline scheduling for a job, the user must code the DEADLINE parameter on a //*MAIN statement. This parameter specifies the time or date by which the user wants the job scheduled. It also specifies which deadline scheduling algorithm JES3 is to use for the job.

The DEADLINE DSP controls the scheduling of these jobs. The DEADLINE DSP examines all the jobs in the deadline queue and issues an ATIME macro instruction for the shortest time interval until a job priority change is required. Unless another job with a shorter time interval is placed in the queue, the DEADLINE DSP waits until the time expires. Then, the priority of the waiting job is increased to increase the probability of the job being processed on time.

If the operator presses the STOP button or enters an MVS™ QUIESCE command, deadline scheduling stops. When the system is restarted, the operator must reinitialize the DEADLINE DSP by entering the *START,DEADLINE command. Reinitializing the DSP resets the deadline scheduling internal clock to the correct time. If the DSP is not reinitialized, the clock continues from the time at which deadline scheduling stopped and jobs in the deadline queue are delayed by the amount of time the system was stopped or quiesced.

If no jobs are in the deadline queue, the DEADLINE DSP sets the ATIME macro instruction to expire at midnight (as a default), and the DEADLINE DSP waits until it is canceled by the operator or until another deadline job is placed on the queue.