Control of priority and instruction rates on a multithreaded processor

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.

1 . A method for assigning a ranking order to a plurality of instruction threads to be executed on a multi-thread processor, comprising the steps of: 
 providing a plurality of metrics required for the establishment of rank order for each thread;    assigning each metric to a set of bits;    assembling the sets of bits in a composite metric with the most important metric being assigned to the most significant bits of the composite metric and the least important metric being assigned to the least significant bits of the composite metric; and    assigning a ranking order to the composite metrics in dependence on their values.    
   
   
       2 . A method according to  claim 1  in which the step of assigning a ranking order to the composite metrics comprises the steps of: 
 comparing a pair of composite metrics and swapping their order if the lower positioned composite metric has a greater or equal value than the higher positioned composite metric.    
   
   
       3 . A method according to  claim 2  in which the step of comparing a pair of composite metric proceeds from the lowest ranked pair to the highest ranked pair of composite metrics.  
   
   
       4 . A method according to  claim 3  in which the process returns to the lowest ranked pair after comparison of the highest ranked pair.  
   
   
       5 . Apparatus for assigning a ranking order to a plurality of instruction threads to be executed on a multi-threaded processor comprising: 
 means for providing a plurality of metrics required for establishment of rank order for a thread;    means for assigning each metric to a set of bits;    means for assembling the sets of bits in a composite metric with the most important metric being assigned to the most significant bits and the least important metric being assigned to the least significant bits; and    assigning a ranking order to the composite metrics in dependence on their values.    
   
   
       6 . Apparatus according to  claim 5  in which the means for assigning a ranking order to the composite metric comprises: 
 means to compare a pair of composite metrics; and    means to swap the ranking order of the pair of composite metrics if the lower positioned composite metric has a greater or equal value than the higher positioned composite metric.    
   
   
       7 . Apparatus according to  claim 6  in which the means to compare composite metrics proceeds from the lowest ranked pair to the highest ranked pair.  
   
   
       8 . Apparatus according to  claim 7  in which the comparison means returns to the lowest ranked pair after comparison of the highest ranked pair.