Cluster Assignment Strategies for a Clustered Trace Cache Processor

This report examines dynamic cluster assignment for a clustered trace cache processor (CTCP). Previously proposed clustering techniques run into unique problems as issue width and cluster count increase. Realistic design conditions, such as variable data forwarding latencies between clusters and a heavily partitioned instruction window also increase the degree of difficulty for effective cluster assignment. In this report, the trace cache and fill unit are used to perform effective dynamic cluster assignment. The retire-time fill unit analysis is aided by a dynamic profiling mechanism embedded within the trace cache. This mechanism provides information on inter-trace trace dependencies and critical inputs, elements absent in previous retire-time CTCP cluster assignment work. The strategy proposed in this report leads to more intra-cluster data forwarding and shorter data forwarding distances. In addition, performing this strategy at retire-time reduces issuetime complexity and eliminates early pipeline stages. This increases overall performance for the SPEC CPU2000 integer programs by 8.4% over our base CTCP architecture. This speedup is significantly higher than a previously proposed retire-time CTCP assignment strategy (1.9%). Dynamic cluster assignment is also evaluated for several alternate cluster designs as well as media benchmarks.