A data cache with multiple caching strategies tuned to different types of locality

The difference-bit cache is a two-way set-associative cache with an access time that is smaller than that of a conventional one and close or equal to that of a direct-mapped cache. This is achieved by noticing that the two tags for a set have to differ at least by one bit and by using this bit to select the way. In contrast with previous approaches that predict the way and have two types of hits (primary of one cycle and secondary of two to four cycles), all hits of the difference-bit cache are of one cycle. The evaluation of the access time of our cache organization has been performed using a recently proposed on-chip cache access model.

The Difference-Bit Cache

The demand for high-performance architectures and powerful battery-operated mobile devices has accentuated the need for low-power systems. In many media and embedded applications, the memory system can consume more than 50p of the overall system energy, making it a ripe candidate for optimization. To address this increasingly important problem, this article studies energy-efficient cache architectures in the memory hierarchy that can have a significant impact on the overall system energy consumption.Existing cache optimization approaches have looked at partitioning the caches at the circuit level and enabling/disabling these cache partitions (subbanks) at the architectural level for both performance and energy. In contrast, this article focuses on partitioning the cache resources architecturally for energy and energy-delay optimizations. Specifically, we investigate ways of splitting the cache into several smaller units, each of which is a cache by itself (called a subcache). Subcache architectures not only reduce the per-access energy costs, but can potentially improve the locality behavior as well.The proposed subcache architecture employs a page-based placement strategy, a dynamic page remapping policy, and a subcache prediction policy in order to improve the memory system energy behavior, especially on-chip cache energy. Using applications from the SPECjvm98 and SPEC CPU2000 benchmarks, the proposed subcache architecture is shown to be very effective in improving both the energy and energy-delay metrics. It is more beneficial in larger caches as well.

Partitioned instruction cache architecture for energy efficiency

A dual data cache system structure, called a cooperative cache system, is designed as a low power cache structure for embedded processors. The cooperative cache system consists of two caches, i.e., a direct-mapped temporal oriented cache (TOC) and a four-way set-associative spatial oriented cache (SOC). These two caches are constructed with different block sizes as well as associativities. The block size of the TOC is 8bytes and that of the SOC is 32bytes, and the capacity of each cache is 8Kbytes. The cooperative cache system achieves improvement in performance and reduces power consumption by virtue of the structural characteristics of the two caches designed inherently to help each other. The cooperative cache system is adopted as the cache structure for the CalmRISC-32 embedded processor that is going to be manufactured by Samsung Electronics Co. with 0.25μm technology.

A power efficient cache structure for embedded processors based on the dual cache structure

A dual data cache system structure, called a cooperative cache system, is designed as a low power cache structure for embedded processors. The cooperative cache system consists of two caches, i.e., a direct-mapped temporal oriented cache (TOC) and a four-way set-associative spatial oriented cache (SOC). These two caches are constructed with different block sizes as well as associativities. The block size of the TOC is 8bytes and that of the SOC is 32bytes, and the capacity of each cache is 8Kbytes. The cooperative cache system achieves improvement in performance and reduces power consumption by virtue of the structural characteristics of the two caches designed inherently to help each other. The cooperative cache system is adopted as the cache structure for the CalmRISC-32 embedded processor that is going to be manufactured by Samsung Electronics Co. with 0.25µm technology.

K. B. Theobald

Papers

A Design Frame for Hybrid Access Cashes