On the effectiveness of prefetching and reuse in reducing L1 data cache traffic: a case study of Snort

Reducing the number of data cache accesses improves performance, port efficiency, bandwidth and motivates the use of single ported caches instead of complex and expensive multi-ported ones. In this paper we consider an intrusion detection system as a target application and study the effectiveness of two techniques - (i) prefetching data from the cache into local buffers in the processor core and (ii) load Instruction Reuse (IR) - in reducing data cache traffic. The analysis is carried out using a microarchitecture and instruction set representative of a programmable processor with the aim of determining if the above techniques are viable for a programmable pattern matching engine found in many network processors. We find that IR is the most generic and efficient technique which reduces cache traffic by up to 60%. However, a combination of prefetching and IR with application specific tuning performs as well as and sometimes better than IR alone.