Processors

Avoiding Cache Thrashing Due to Private Data Placement in Last-Level Cache for Manycore Scaling

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Executive Summary

Without high-bandwidth broadcast, large numbers of cores require a scalable point-to-point interconnect and a directory protocol. In such cases, a shared, inclusive Last Level Cache (LLC) can improve data sharing and avoid three way communications for shared reads. However, if inclusion encompasses thread-private data, two problems arise with the shared LLC. First, current memory allocators align stack bases on page boundaries, which emerge as a source of severe conflict misses for large numbers of threads on data-parallel applications. Second, correctness does not require the private data to reside in the shared directory or the LLC. This paper advocates stack-base randomization that eliminates the major source of conflict misses for large numbers of threads.

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