NDLI: Runahead execution: an alternative to very large instruction windows for out-of-order processors

Content Provider	IEEE Xplore Digital Library
Author	Mutlu, O. Stark, J. Wilkerson, C. Patt, Y.N.
Copyright Year	2003
Description	Author affiliation: Dept. of Electr. & Comput. Eng., Texas Univ., Austin, TX, USA (Mutlu, O.)
Abstract	Today's high performance processors tolerate long latency operations by means of out-of-order execution. However, as latencies increase, the size of the instruction window must increase even faster if we are to continue to tolerate these latencies. We have already reached the point where the size of an instruction window that can handle these latencies is prohibitively large in terms of both design complexity and power consumption. And, the problem is getting worse. This paper proposes runahead execution as an effective way to increase memory latency tolerance in an out-of-order processor without requiring an unreasonably large instruction window. Runahead execution unblocks the instruction window blocked by long latency operations allowing the processor to execute far ahead in the program path. This results in data being prefetched into caches long before it is needed. On a machine model based on the Intel/spl reg/ Pentium/spl reg/ processor, having a 128-entry instruction window, adding runahead execution improves the IPC (instructions per cycle) by 22% across a wide range of memory intensive applications. Also, for the same machine model, runahead execution combined with a 128-entry window performs within 1% of a machine with no runahead execution and a 384-entry instruction window.
Sponsorship	IEEE Comput. Soc. Tech. Committee on Comput. Architecture
Starting Page	129
Ending Page	140
File Size	305131
Page Count	12
File Format	PDF
ISBN	0769518710
ISSN	15300897
DOI	10.1109/HPCA.2003.1183532
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2003-02-12
Publisher Place	USA
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Out of order Delay Windows Prefetching Energy consumption Engines Trademarks Hardware Microprocessors Software
Content Type	Text
Resource Type	Article

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