A large fraction of the microprocessor energy is consumed by the data movement in the system. One of the reasons is the inefficiency in the conventional cache design. Cache blocks larger than a word are used in conventional caches to exploit spatial locality. However, many applications only use a small part of a cache block before its eviction. Transferring and storing unused data wastes bandwidth, energy, and limited cache space. Prior work on fine-grained caches can reduce data access and storage granularity to reduce the amount of unused data. However, small data blocks typically require greater metadata and control overhead. Sharing the common bits among tags of fine-grained blocks can reduce the metadata overhead but the constraints on which fine-grained blocks can share tag bits can cause fragmentation. This work proposes scrabble, a fine-grained cache that can merge multiple non-contiguous fine-grained blocks into a variable size merged block. The length of the shared tag is maximized to reduce the metadata overhead. The space utilization is improved by supporting merged blocks with variable size. The control overhead can be reduced by moving the merged block together from memory to the last level cache. For applications with poor spatial locality, Scrabble cache can achieve more than 40 percent of performance improvement. Even for application with good spatial locality, the speedup is still more than 7 percent. In general, for an evaluated set of benchmarks, Scrabble cache achieves an average of 2.41× effective capacity over the baseline cache with the same cache capacity which leads to a 16.7 percent performance improvement and an 11 percent on-chip energy reduction. As compared to a state-of-the-art fine-grained cache, Scrabble cache achieves a 1.25× effective capacity, a 7.9 percent speedup, and a 5.8 percent on-chip energy reduction.

中文翻译：

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Scrabble：具有自适应合并块的细粒度缓存

系统中的数据移动消耗了微处理器能量的很大一部分。原因之一是传统缓存设计效率低下。在传统缓存中使用大于一个字的缓存块来利用空间局部性。但是，许多应用程序在驱逐之前仅使用缓存块的一小部分。传输和存储未使用的数据会浪费带宽、能源和有限的缓存空间。先前关于细粒度缓存的工作可以减少数据访问和存储粒度，从而减少未使用的数据量。然而，小数据块通常需要更大的元数据和控制开销。在细粒度块的标签之间共享公共位可以减少元数据开销，但细粒度块可以共享标签位的限制会导致碎片。这项工作提出了拼字游戏，一种细粒度缓存，可以将多个不连续的细粒度块合并成一个可变大小的合并块。共享标签的长度被最大化以减少元数据开销。通过支持可变大小的合并块来提高空间利用率。通过将合并的块一起从内存移动到最后一级缓存，可以减少控制开销。对于空间局部性较差的应用，Scrabble 缓存可以实现 40% 以上的性能提升。即使对于具有良好空间局部性的应用程序，加速仍然超过 7%。一般而言，对于一组评估的基准，Scrabble 缓存在相同缓存容量的情况下实现了平均 2.41 倍于基准缓存的有效容量，这导致 16.7% 的性能提升和 11% 的片上能源降低。