Data processing system and method for predictively selecting a scope of broadcast of an operation utilizing a history-based prediction

Abstract

According to a method of data processing, a predictor is maintained that indicates a historical scope of broadcast for one or more previous operations transmitted on an interconnect of a data processing system. A scope of broadcast of a subsequent operation is predictively selected by reference to the predictor.

1 . A cache memory for a data processing system including an interconnect fabric and at least first and second coherency domains each containing at least one processing unit, said cache memory comprising:
 a data array;   a cache directory of contents of said data array; and   a cache controller including scope prediction logic, said scope prediction logic further including:   a plurality of predictors each indicating a historical scope of broadcast on the interconnect fabric for one or more previous operations of a respective one of a plurality of operation classes;   index generation logic that, responsive to receipt of a set of read input characterizing a prospective bus operation to be issued, generates a read index to select a scope prediction indication by one of said plurality of predictors for use in transmission of said prospective bus operation; and   update logic that, responsive to receipt of a combined response to a successfully completed bus operation, generates an update to one of said plurality of predictors in accordance with a location of a servicing snooper in said data processing system.   
   
   
       2 . A data processing system, comprising:
 at least first and second coherency domains each containing at least one processing unit including a cache memory;   an interconnect fabric coupling said first and second coherency domains; and   scope prediction logic within the first coherency domain, said scope prediction logic including a predictor that indicates a historical scope of broadcast for one or more previous operations transmitted on the interconnect fabric, wherein said scope prediction logic predictively selects a scope of broadcast of a subsequent operation by reference to said predictor if said operation is of a first predetermined operation type and predictively selects a scope of broadcast of said operation by reference to a coherency state of a target memory address of said operation if said operation is of a second predetermined operation type.   
   
   
       3 . The data processing system of  claim 2 , wherein said scope prediction logic predictively selects a first scope of broadcast including both said first and second coherency domains in response to a first setting of said predictor and selects a second scope of broadcast including said first coherency domain and excluding said second coherency domain in response to a second setting of said predictor. 
   
   
       4 . The data processing system of  claim 2 , wherein said cache memory of said first coherency domain includes said scope prediction logic. 
   
   
       5 . The data processing system of  claim 2 , wherein said scope prediction logic includes a plurality of predictors that each indicates a historical scope of broadcast of operations in a respective one of a plurality of operation classes. 
   
   
       6 . The data processing system of  claim 2 , wherein said predictor comprises a saturating counter that saturates toward a prediction of a narrower broadcast scope. 
   
   
       7 . The data processing system of  claim 6 , wherein said scope prediction logic includes a mode field, and wherein said scope prediction logic reverses a prediction indicated by said saturating counter in response to a setting of said mode field. 
   
   
       8 . A cache memory for a data processing system including an interconnect fabric and at least first and second coherency domains each containing at least one processing unit, said cache memory comprising:
 a data array;   a cache directory of contents of said data array; and   a cache controller including scope prediction logic, wherein said scope prediction logic includes a predictor that indicates a historical scope of broadcast for one or more previous operations transmitted by said cache memory on the interconnect fabric, wherein said scope prediction logic predictively selects a scope of broadcast of a subsequent operation by reference to said predictor if said operation is of a first predetermined operation type and predictively selects a scope of broadcast of said operation by reference to a coherency state of a target memory address of said operation recorded in said cache directory if said operation is of a second predetermined operation type.   
   
   
       9 . The cache memory of  claim 8 , wherein said scope prediction logic predictively selects a first scope of broadcast including both said first and second coherency domains in response to a first setting of said predictor and selects a second scope of broadcast including said first coherency domain and excluding said second coherency domain in response to a second setting of said predictor. 
   
   
       10 . The cache memory of  claim 8 , wherein said scope prediction logic includes a plurality of predictors that each indicates a historical scope of broadcast of operations in a respective one of a plurality of operation classes. 
   
   
       11 . The cache memory of  claim 8 , wherein said predictor comprises a saturating counter that saturates toward a prediction of a narrower broadcast scope. 
   
   
       12 . A processing unit, comprising:
 a cache memory in accordance with  claim 8 ; and   at least one processor core coupled to said cache memory.