Core-Selectability in Chip Multiprocessors

Hashem H. Najaf-abadi, Niket K. Choudhary and Eric Rotenberg

The centralized structures necessary for the extraction of instruction-level parallelism (ILP) are consuming progressively smaller portions of the total die area of chip multiprocessors (CMP). The reason for this is that scaling these structures does not enhance general performance as much as scaling the cache and interconnect. However, the fact that these structures now consume less proportional die area opens an avenue to enhancing their performance through truly overcoming the one-size-fits-all approach to their design. This paper proposes core-selectability – incorporating differently designed cores that can be toggled into active employment. This enables differently customized ILP-extracting structures to be at hand in the system while not dramatically adding to the interconnect complexity. The design verification effort is minimized by separating the complexity of different core designs. Moreover, contrary to alternative approaches, the performance and power efficiency of the core designs are not compromised.

Evaluation results are presented that show that, even when limiting the diversity between core designs to only the sizing of microarchitectural structures, core-selectability has the potential to provide notable performance enhancement (with an average of 10%) to scalable multithreaded applications, without increased concurrency. In addition, it can provide significantly greater throughput to multiprogrammed workloads by providing the potential for the system to transform into a heterogeneous design.

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