Processor Set Contradictions

Processor Set Contradictions

You can create contradictions using the pset command. For example, you can assign a processor set to the gang-scheduled queue, and also assign a normal or real-time process to that same processor set. Since the assigned process is not gang-scheduled, it will never appear in the queue that the processor group can service. Since the process is assigned to that group, it can run on no other CPUs. Accordingly, the process never runs at all. You have to change one of the assignments before the process can even terminate.

It is also possible to create an empty set, one with no CPUs assigned to it. Processes or queues that depend on that set simply do not execute. Some users consider this to be a feature, not an problem. For example, if the processor set servicing the batch queue is made empty, batch-queue work--even active, half-completed programs--simply sit and do not execute. At some later time, pset can be used to take CPUs from some other processor set and reassign them to the batch queue set, at which time the unserviced jobs begin to execute again.