通过硬件一致性哈希机制实现大型DRAM缓存的有效动态调整大小
Enabling Efficient Dynamic Resizing of Large DRAM Caches via A Hardware Consistent Hashing Mechanism
摘要：
已经提出将裸片堆叠式DRAM用作具有数百或数千兆字节容量的大型、高带宽、末级高速缓冲存储器。然而，并非所有工作负载（或阶段）都可以有效地利用这么多缓存空间。不幸的是，未使用（或未充分使用）的高速缓存由于外围电路中的泄漏和周期性DRAM刷新而继续消耗功率。动态调整可用的DRAM缓存容量可以在很大程度上消除这种能量开销。然而，当前提出的DRAM高速缓存组织为动态高速缓存缓存管理引入了新的挑战。该组织不同于传统的SRAM高速缓存组织，因为它将整个高速缓存集及其标签放置在单个存储体中，以减少片上面积和功耗开销。因此，对DRAM高速缓存进行重映射需要将集合从断电的存储体重映射到活动存储体。在本文中，我们提出CRUNCH（缓存调整使用本地一致性哈希），硬件数据重新映射方案的启发一致性哈希，最初提出的算法，以统一和动态地分布互联网流量在不断变化的人口的Web服务器。CRUNCH提供了将数据从断电的银行单独重新映射到活动银行的负载平衡重新映射，而不需要重新映射所有银行的数据集，这与实现负载均衡的天真方案不同。CRUNCH仅重新映射掉电存储体的集合，因此它以低存储体上电/掉电转换延迟实现这种负载均衡。CRUNCH将良好的负载均衡和低转换延迟相结合，为实现高效的DRAM高速缓存存储提供了基础。
英文摘要：
Die-stacked DRAM has been proposed for use as a large, high-bandwidth, last-level cache with hundreds or thousands of megabytes of capacity. Not all workloads (or phases) can productively utilize this much cache space, however. Unfortunately, the unused (or under-used) cache continues to consume power due to leakage in the peripheral circuitry and periodic DRAM refresh. Dynamically adjusting the available DRAM cache capacity could largely eliminate this energy overhead. However, the current proposed DRAM cache organization introduces new challenges for dynamic cache resizing. The organization differs from a conventional SRAM cache organization because it places entire cache sets and their tags within a single bank to reduce on-chip area and power overhead. Hence, resizing a DRAM cache requires remapping sets from the powered-down banks to active banks. In this paper, we propose CRUNCH (Cache Resizing Using Native Consistent Hashing), a hardware data remapping scheme inspired by consistent hashing, an algorithm originally proposed to uniformly and dynamically distribute Internet traffic across a changing population of web servers. CRUNCH provides a load-balanced remapping of data from the powered-down banks alone to the active banks, without requiring sets from all banks to be remapped, unlike naive schemes to achieve load balancing. CRUNCH remaps only sets from the powered-down banks, so it achieves this load balancing with low bank power-up/down transition latencies. CRUNCH's combination of good load balancing and low transition latencies provides a substrate to enable efficient DRAM cache resizing.
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