Lowering the Hit Latencies of Low Voltage Caches Based on the Cross-Sensing Timing Speculation SRAM

Abstract

The probability of timing failure in SRAM accessing becomes unacceptably high at low voltages, which makes the SRAM become the bottleneck of the system performance. Recently proposed timing speculation SRAM (SSRAM) can access bit cells much earlier than the conservative time margin and detect the potential timing failures. Unfortunately, the performance benefit brought by this speculative scheme might be nullified by the extra cycles used to correct the errors. Therefore, in a cache architecture, cachelines containing bit cells with timing failure bring significant performance degradation in a low-voltage scenario. In this paper, we propose the set-associative L1 and L2 Remapping and Reuse-aware timing Speculation caches (RRS caches) based on the cross-sensing SSRAM to reduce the weak cacheline access penalties under low supply voltages. RRS caches improve the proportion of the error-free cachelines (or strong cachelines) by clustering as more as possible bit cells with timing failures into weak cachelines. In addition, RRS caches swap the frequently reused data to the error-free cachelines to further reduce the average access latency and the energy consumption by an optimized filling/replacement policy. We compared the performance, energy consumption and area overhead of RRS caches with those of state-of-the-art approaches. According to our simulation results, RRS caches improve the system performance close to that of the Perfect caches in a four-core processor with only 0.12% extra energy consumption, 4.12% extra area overhead in the L1 cache and 2.69% extra energy consumption, 5.66% extra area overhead in the L2 cache compared to the cache designs with the raw SSRAM.

Keywords

• Cacheline remapping
• low-voltage cache
• near-threshold voltage
• replacement policy
• timing speculation SRAM