NDLI: Value locality and load value prediction (OPSR, Vol. 30, Issue. 5)

Content Provider	ACM Digital Library
Author	Shen, John Paul Lipasti, Mikko H. Wilkerson, Christopher B.
Abstract	Since the introduction of virtual memory demand-paging and cache memories, computer systems have been exploiting spatial and temporal locality to reduce the average latency of a memory reference. In this paper, we introduce the notion of value locality, a third facet of locality that is frequently present in real-world programs, and describe how to effectively capture and exploit it in order to perform load value prediction. Temporal and spatial locality are attributes of storage locations, and describe the future likelihood of references to those locations or their close neighbors. In a similar vein, value locality describes the likelihood of the recurrence of a previously-seen value within a storage location. Modern processors already exploit value locality in a very restricted sense through the use of control speculation (i.e. branch prediction), which seeks to predict the future value of a single condition bit based on previously-seen values. Our work extends this to predict entire 32- and 64-bit register values based on previously-seen values. We find that, just as condition bits are fairly predictable on a per-static-branch basis, full register values being loaded from memory are frequently predictable as well. Furthermore, we show that simple microarchitectural enhancements to two modern microprocessor implementations (based on the PowerPC 620 and Alpha 21164) that enable load value prediction can effectively exploit value locality to collapse true dependencies, reduce average memory latency and bandwidth requirements, and provide measurable performance gains.
Starting Page	138
Ending Page	147
Page Count	10
File Format	PDF
ISSN	01635980
DOI	10.1145/248208.237173
Journal	ACM SIGOPS Operating Systems Review (OPSR)
Volume Number	30
Issue Number	5
Language	English
Publisher	Association for Computing Machinery (ACM)
Publisher Date	1975-04-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Content Type	Text
Resource Type	Article
Subject	Computer Networks and Communications Hardware and Architecture Information Systems

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