Partitioned first-level cache design for clustered microarchitectures

ABSTRACT

The high clock frequencies of modern superscalar processors make the wire delay incurred in moving data across the processor chip a significant concern. As frequencies continue to increase, it will become more difficult for a centralized first level data cache to supply the timely data bandwidth required by superscalar processors.This paper presents a complete solution for the partitioning of the first level of the memory hierarchy. The first level data cache is split into several independent partitions, which are arbitrarily distributable across the processor die. After being decoded, memory instructions are sent to the reservation stations of the functional unit adjacent to the cache partition that they are most likely to access. The partition assignments for both static instructions and cache data are dynamically changed to adapt to data access patterns. A data cache line is permitted to reside in only one partition at a time, allowing each store to update only a single partition, and allowing the partitioning and simplification of the memory disambiguation logic. The partitioned cache achieves a reduction in cache access latency through a combination of reduced wire delay and reduced cache array size. A partitioned cache with eight 8KB direct-mapped partitions maintains a hit rate greater than that of a 32KB direct-mapped cache. A machine utilizing the partitioned cache outperforms a machine with a conventional 64KB direct-mapped cache by 4.5% and a machine with a 64KB 8-way set-associative cache by 7.0%, when cache latencies estimated through the use of the CACTI cache simulation tool are taken into account.

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INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.1 PROCESSOR ARCHITECTURES
      C.1.1 Single Data Stream Architectures

Additional Classification:
  B. Hardware
  B.3 MEMORY STRUCTURES
      B.3.m Miscellaneous

General Terms:
Design, Performance

Keywords:
clustered microarchitecture, partitioned cache