An L2 Cache Architecture Supporting Bypassing for Low Energy and High Performance

Conventional 2-level cache architecture is not efficient in mobile systems when small programs that do not require the large L2 cache run. Bypassing the L2 cache for those small programs has two benefits. When only a single program runs, bypassing the L2 cache allows to power it down removing its leakage energy consumption. When multiple programs run simultaneously on multiple cores, small programs bypass the L2 cache while large programs use it. This decreases conflicts in the L2 cache among those programs increasing overall performance. From our experiments using cycle-accurate performance and energy simulators, our proposed L2 cache architecture supporting bypassing is shown to be effective in reducing L2 cache energy consumption and increasing overall performance of programs.

Execution Model to Reduce the Interference of Shared Memory in ARINC 653 Compliant Multicore RTOS

Multicore architecture is applied to contemporary avionics systems to deal with complex tasks. However, multicore architectures can cause interference by contention because the cores share hardware resources. This interference reduces the predictable execution time of safety-critical systems, such as avionics systems. To reduce this interference, methods of separating hardware resources or limiting capacity by core have been proposed. Existing studies have modified kernels to control hardware resources. Additionally, an execution model has been proposed that can reduce interference by adjusting the execution order of tasks without software modification. Avionics systems require several rigorous software verification procedures. Therefore, modifying existing software can be costly and time-consuming. In this work, we propose a method to apply execution models proposed in existing studies without modifying commercial real-time operating systems. We implemented the time-division multiple access (TDMA) and acquisition execution restitution (AER) execution models with pseudo-partition and message queuing on VxWorks 653. Moreover, we propose a multi-TDMA model considering the characteristics of the target hardware. For the interference analysis, we measured the L1 and L2 cache misses and the number of main memory requests. We demonstrated that the interference caused by memory sharing was reduced by at least 60% in the execution model. In particular, multi-TDMA doubled utilization compared to TDMA and also reduced the execution time by 20% compared to the AER model.

Poluição de Cache e Thrashing em Aplicações Paralelas de Alto Desempenho

Conforme os processadores evoluem, o desempenho dos sistemas computacionais se torna cada vez mais limitado pelo tempo de acesso à memória. Caches são empregadas a fim de contornar este problema, mas é necessária uma gerência inteligente dos dados que são armazenados nelas para impedir que problemas como poluição e thrashing degradem seu desempenho. Neste trabalho é apresentada uma análise da poluição de cache e thrashing em aplicações paralelas de alto desempenho. Os resultados mostram que caches com maior associatividade sofrem mais com estes problemas. Até 28% dos cache misses na L1 poderiam ser evitados com uma política de substituição de cache mais inteligente, chegando a até 62% na cache L2 e 98% na LLC. As processors evolve, the performance of computer systems becomes increasingly limited by the memory access time. Caches are employed in order to get around this problem, but an intelligent management of the data that is stored in them is necessary to prevent problems such as pollution and thrashing from degrading their performance. In this work, an analysis of cache and thrashing pollution in high performance parallel applications is presented. The results show that caches with greater associativity suffer more from these problems. Up to 28% of cache misses in the L1 cache could be avoided with a smarter replacement policy, up to 62% in the L2 cache and 98% in the LLC.

A Varying Processor Cache Sets Architecture

Any processor cache has three parameters capacity, line size and associativity. Usually all three are fixed at design time. Algorithms to have variable cache sets are proposed in literature. This paper proposes a method to have variable cache sets logically. The cache comes with fixed sets. The cache is visualized to have logically any number of sets greater than or equal to one. An algorithm for line placement/replacement is proposed in this paper for this model. The proposed model is simulated with SPEC2K benchmarks using Simplescalar Toolkit for two level inclusive set associative cache system. A power saving of 8.4% for L1 cache size 512x4, 17.58% for 1024x4 and 31.3% for 2048x4 is observed compared with traditional set associative cache of same size. A power saving of 7.53% compared with model proposed in literature for L1 size 512x4, 7.64% for 1024x4 and 7.645% for 2048x4 is observed. The L2 cache size is fixed at 2048x8. The average memory access time (AMAT) is found to degrade compared with conventional set associative cache by 19.63% for L1 size of 512x4, 24.68% for 1024x4 and 2048x4. (Abstract)