Thread instruction issue pool counter decremented upon execution and incremented at desired issue rate

Abstract

A method and apparatus for controlling issue rate of instructions for an instruction thread to be executed by a processor is provided. The rate at which instructions are to be executed for an instruction thread are stored and requests are issued to cause instructions to execute in response to the stored rate. The rate at which instruction requests are issued is reduced in response to instruction executions and is increased in the absence of instruction executions. In a multi-threaded processor, instruction rate is controlled by storing the average rate at which each thread should execute instructions. A value representative of the number of instructions available and not yet issued is monitored and is decreased in response to instruction executions. Execution of instructions is prevented on a thread if the number of instructions available but not yet issued falls below a defined value. A ranking order is assigned to a plurality of instructions threads for execution on a multi-threaded processor. A plurality of metrics related to the threads and required for establishment of the rank order are provided. Each metric is assigned to a set of bits and these are assembled in a composite metric being assigned to the most significant bits and the least important metric being assigned to the least significant bits. A ranking order is then assigned to the composite metrics in dependence on their values.