Optimum power efficient shifting algorithm for schedulers

Abstract

A method and mechanism for managing shifts in a shifting queue. A reservation station in a processing device includes a queue of shifting entries. On a given cycle, zero, one, or two instructions may be dispatched and stored in the queue. Depending upon the dispatch conditions and the state of the queue, existing entries within the queue may be shifted to make room for the newly dispatched instruction(s) at the top of the queue. Shift vectors are generated which identify entries of the queue which are to be shifted and by how much. A queue management approach is adopted in which three rules are generally followed: (i) Only shift entries that must shift due to dispatch pressure from above; (ii) If an entry must be shifted elsewhere, shift it as far down the array as the particular implementation allows; and (iii) Don't allow the previous conditions to force additional entries to shift that are not required to shift by dispatch pressure.