A Case for Clumsy Packet Processors

Hardware faults can occur in any computer system. Although faults cannot be tolerated for most systems (e.g., servers or desktop processors), many applications (e.g., networking applications) provide robustness in software. However, processors do not utilize this resiliency, i.e., regardless of the application at hand, a processor is expected to operate completely fault-free. In this paper, we will question this traditional approach of complete correctness and investigate possible performance and energy optimizations when this correctness constraint is released. We first develop a realistic model that estimates the change in the fault rates according to the clock frequency of the cache. Then, we present a scheme that dynamically adjusts the clock frequency of the data caches to achieve the desired optimization goal, e.g., reduced energy or reduced access latency. Finally, we present simulation results investigating the optimal operation frequency of the data caches, where reliability is compromised in exchange of reduced energy and increased performance. Our simulation results indicate that the clock frequency of the data caches can be increased as much as 4 times without incurring a major penalty on the reliability. This also results in 41% reduction in the energy consumed in the data caches and a 24% reduction in the energy-delay-fallibility product.