Revisiting virtual L1 caches: A practical design using dynamic synonym remapping
Revisiting virtual L1 caches: A practical design using dynamic synonym remapping
复制标题
重新审视虚拟 L1 缓存：使用动态同义词重新映射的实用设计
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
G. Sohi
中科院分区：
文献类型：
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作者：
Hongil Yoon;G. Sohi
虚拟高速缓存具有比物理高速缓存更低的访问延迟和能耗，因为它们在高速缓存访问之前不咨询TLB。然而，它们在商业设计中并不流行。问题的关键是同义词的可能性。本文提出了几个经验观察的时间特征的同义词，特别是在缓存的大小是典型的L1缓存。通过利用这些观察结果，本文提出了一种L1虚拟缓存的实用设计，该设计（1）动态地为映射到同一物理页面的所有同义虚拟页面决定唯一的虚拟页面编号，并且（2）使用该唯一的页面编号来放置和查找虚拟缓存中的数据。对这一唯一页码的访问无需任何干预。对其他同义页的访问被动态检测，并被重新映射到对应的唯一虚拟页号，以正确地访问该高速缓存中的数据。由于同义词的时间属性，这种重新映射操作很少见，允许具有动态同义词重新映射的虚拟缓存（VC-DSR）实现虚拟缓存的大部分好处，但无需软件参与。基于真实的应用程序的实验结果表明，VC-DSR可以实现约92%的动态能量节省TLB查找，和99.4%的理想（但不切实际的）虚拟缓存的延迟效益所考虑的配置。
Virtual caches have potentially lower access latency and energy consumption than physical caches because they do not consult the TLB prior to cache access. However, they have not been popular in commercial designs. The crux of the problem is the possibility of synonyms. This paper makes several empirical observations about the temporal characteristics of synonyms, especially in caches of sizes that are typical of L1 caches. By leveraging these observations, the paper proposes a practical design of an L1 virtual cache that (1) dynamically decides a unique virtual page number for all the synonymous virtual pages that map to the same physical page and (2) uses this unique page number to place and look up data in the virtual caches. Accesses to this unique page number proceed without any intervention. Accesses to other synonymous pages are dynamically detected, and remapped to the corresponding unique virtual page number to correctly access data in the cache. Such remapping operations are rare, due to the temporal properties of synonyms, allowing a Virtual Cache with Dynamic Synonym Remapping (VC-DSR) to achieve most of the benefits of virtual caches but without software involvement. Experimental results based on real world applications show that VC-DSR can achieve about 92% of the dynamic energy savings for TLB lookups, and 99.4% of the latency benefits of ideal (but impractical) virtual caches for the configurations considered.