NDLI: Register write specialization register read specialization: a path to complexity-effective wide-issue superscalar processors

Content Provider	IEEE Xplore Digital Library
Author	Seznec, A. Toullec, E. Rochecouste, O.
Copyright Year	2002
Description	Author affiliation: IRISA/INRIA, France (Seznec, A.; Toullec, E.; Rochecouste, O.)
Abstract	With the continuous shrinking of transistor size, processor designers are facing new difficulties to achieve high clock frequency. The register file read time, the wake up and selection logic traversal delay and the bypass network transit delay with also their respective power consumptions constitute major difficulties for the design of wide issue superscalar processors. In this paper, we show that transgressing a rule, that has so far been applied in the design of all the superscalar processors, allows to reduce these difficulties. Currently used general-purpose ISAs feature a single logical register file (and generally a floating-point register file). Up to now all superscalar processors have allowed any general-purpose functional unit to read and write any physical general purpose register. First, we propose Register Write Specialization, i.e, forcing distinct groups of functional units to write only in distinct subsets of the physical register file, thus limiting the number of write ports on each individual register. Register Write Specialization significantly reduces the access time, the power consumption and the silicon area of the register file without impairing performance. Second, we propose to combine Register Write Specialization with Register Read Specialization for clustered superscalar processors. This limits the number of read ports on each individual register and simplifies both the wakeup logic and the bypass network. With a 8-way 4-cluster WSRS architecture, the complexities of the wake-up logic entry and bypass point are equivalent to the ones found with a conventional 4-way issue processor. More physical registers are needed in WSRS architectures. Nevertheless, using WSRS architecture allows a dramatic reduction of the total silicon area devoted to the physical register file (by a factor four to six). Its power consumption is more than halved and its read access time is shortened by one third. Some extra hardware and/or a few extra pipeline stages are needed for register renaming. WSRS architecture induces constraints on the policy for allocating instructions to clusters. However, performance of a 8-way 4-cluster WSRS architecture stands the comparison with the one of a conventional 8-way 4-cluster conventional superscalar processor.
Sponsorship	IEEE TC-uArch ACM SIGMICRO Hewlett Packard IBM and IBM Turk Intel and Intel Turkey Microsoft Nat. Sci. Found
Starting Page	383
Ending Page	394
File Size	301345
Page Count	12
File Format	PDF
ISBN	0769518591
ISSN	10724451
DOI	10.1109/MICRO.2002.1176265
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2002-11-18
Publisher Place	Turkey
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Registers Meteorological radar Energy consumption Delay effects Silicon Logic Transistors Process design Clocks Frequency
Content Type	Text
Resource Type	Article

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