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Deconstructing commit
Austin, TX, USA March 10-March 12
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/ISPASS.2004.12913572004 IEEE International Symposium on ...
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G.B. Bell, Dept. of Elec. & Comp. Engr., Wisconsin-Madison Univ., Madison, WI, USA
M.H. Lipasti, Dept. of Elec. & Comp. Engr., Wisconsin-Madison Univ., Madison, WI, USA
Many modern processors execute instructions out of their original program order to exploit instruction-level parallelism and achieve higher performance. However even though instructions can execute in an arbitrary order, they must eventually commit, or retire from execution, in program order. This constraint provides a safety mechanism to ensure that mis-speculated instructions are not inadvertently committed, but can consume valuable processor resources and severely limit the degree of parallelism exposed in a program. We assert that such a constraint is overly conservative, and propose conditions under which it can be relaxed. This paper deconstructs the notion of commit in an out-of-order processor, and examines the set of necessary conditions under which instructions can be permitted to retire out of program order. It provides a detailed analysis of the frequency and relative importance of these conditions, and discusses microarchitectural modifications that relax the in-order commit requirement. Overall, we found that for a given set of processor resources our technique achieves speedups of up to 68% and 8% for floating point and integer benchmarks, respectively. Conversely, because out-of-order commit allows more efficient utilization of cycle-time limiting resources, it can alternatively enable simpler designs with potentially higher clock frequencies.
Citation:
G.B. Bell, M.H. Lipasti, "Deconstructing commit," ispass, pp.68-77, 2004 IEEE International Symposium on Performance Analysis of Systems and Software (ISPASS'04), 2004
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