1999 International Conference on Parallel Architectures and Compilation Techniques (Cat. No.PR00425) (1999)
Newport Beach, California
Oct. 12, 1999 to Oct. 16, 1999
Pierre Michaud , IRISA/INRIA
Andre Seznec , IRISA/INRIA
Stephan Jourdan , Intel Corporation
The effective performance of wide-issue superscalar processors depends on many parameters, such as branch prediction accuracy, available instruction-level parallelism, and instruction-fetch bandwidth. This paper explores the relations between some of these parameters, and more particularly, the requirement in instruction-fetch bandwidth.We introduce new enhancements to boost effectively the instruction-fetch bandwidth of conventional fetch engines. However, experiments strongly show that performance improves less for a given instruction-fetch bandwidth gain as the base fetch bandwidth increases. At the level of bandwidth exhibited by the proposed schemes, the performance improvement is small. This clearly brings to light potential relations between the fetch bandwidth and the other parameters.We provide a model to explain this behavior and quantify some relations. Based on the experimental observation that the available parallelism in an instruction window of size N grows as the square root of N, we derive from the model that the instruction fetch bandwidth requirement increases as the square root of the distance between mispredicted branches. We also show that the instruction fetch bandwidth requirement increases linearly with the parallelism available in a fixed-size instruction window.
superscalar processors, instruction fetch, branch prediction, instruction-level parallelism
A. Seznec, S. Jourdan and P. Michaud, "Exploring Instruction-Fetch Bandwidth Requirement in Wide-Issue Superscalar Processors," 1999 International Conference on Parallel Architectures and Compilation Techniques (Cat. No.PR00425)(PACT), Newport Beach, California, 1999, pp. 2.