Kenneth Mark Wilson

Increasing Cache Port Efficiency for Dynamic Superscalar Microprocessors

The memory bandwidth demands of modern microprocessors require the use of a multi-ported cache to achieve peak performance. However, multi-ported caches are costly to implement. In this paper we propose techniques for improving the bandwidth of a single cache port by using additional buffering in the processor, and by taking maximum advantage of a wider cache port. We evaluate these techniques using realistic applications that include the operating system. Our techniques using a single-ported cache achieve 91% of the performance of a dual-ported cache.

High bandwidth on-chip cache design

In this paper, we evaluate the performance of high bandwidth cache organizations employing multiple cache ports, multiple cycle hit times, and cache port efficiency enhancements, such as load all and line buffer, to find the organization that provides the best processor performance. Using a dynamic superscalar processor running realistic benchmarks that include operating system references, we use execution time to measure processor performance. When the cache is limited to a single cache port without enhancements, we find that two cache ports increase processor performance by 25 percent. With the addition of line buffer and load all to a single pelted cache, the processor achieves 91 percent of the performance of the same processor containing a cache with two ports. When the processor is not limited to a single cache port, the results show that a large dual-ported multicycle pipelined SRAM cache with a line buffer maximizes processor performance. A large pipelined cache provides both a low miss rate and a high CPU clock frequency. Dual-porting the cache and using a line buffer provide the bandwidth needed by a dynamic superscalar processor. The line buffer makes the pipelined dual-ported cache the best option by increasing cache port bandwidth and hiding cache latency.