Determining each stall reason for each stalled instruction within a group of instructions during a pipeline stall

Abstract

During a pipeline stall in a processor, until a next to complete instruction group completes, a monitoring unit receives, from a completion unit of a processor, a next to finish indicator indicating the finish of an oldest previously unfinished instruction from among a plurality of instructions of a next to complete instruction group. The monitoring unit receives, from functional units of the processor, finish reports including completion reasons for separate instructions. The monitoring unit determines at least one stall reason from among multiple stall reasons for the oldest instruction from a selection of completion reasons from a selection of finish reports aligned with the next to finish indicator from among the finish reports. Once the monitoring unit receives a complete indicator from the completion unit, indicating the completion of the next to complete instruction group, the monitoring unit stores each determined stall reason aligned with each next to finish indicator in memory.