A Dynamic Multithreading Processor

Abstract

We present an architecture that features dynamic multithreading execution of a single program. Threads are created automatically by hardware at procedure and loop boundaries and executed speculatively on a simultaneous multithreading pipeline. Data prediction is used to alleviate dependency constraints and enable lookahead execution of the threads. A two-level hierarchy significantly enlarges the instruction window. Eficient selective recovery from the second level instruction window takes place after a mispredicted input to a thread is corrected. The second level is slower to access but has the advantage of large storage capacity. We show several advantages of this architecture: (1) it minimizes the impact of ICache misses and branch mispredictions by fetching and dispatching instructions out-of-order, (2) it uses a novel value prediction and recovery mechanism to reduce artt$cial data dependencies created by the use of a stack to manage run-time storage, and (3) it improves the execution throughput of a superscalar by 15 % without increasing the execution resources or cache bandwidth, and by 30 % with one additional ICache fetch port. The speedup was measured on the integer SPEC95 benchmarks, without any compiler support, using a detailed peqormance simulator,