Reorder Buffer Structure with Shelter Buffer for Out-of-Order Issue Superscalar Processors

Mun-Suek CHANG  Choung-Shik PARK  Sang-Bang CHOI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E83-A    No.6    pp.1091-1099
Publication Date: 2000/06/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section of Papers Selected from 1999 International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC'99))
superscalar processor,  out-of-order issue,  reorder buffer,  stagnation,  shelter buffer,  

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The reorder buffer is usually employed to maintain the instruction execution in the correct order for a superscalar pipeline with out-of-order issue. In this paper, we propose a reorder buffer structure with shelter buffer for out-of-order issue superscalar processors not only to control stagnation efficiently, but also to reduce the buffer size. We can get remarkable performance improvement with only one or two buffers. Simulation results show that if the size of reorder buffer is between 8 and 32, performance gain obtained from the shelter is noticeable. For the shelter buffer of size 4, there is no performance improvement compared to that of size 2, which means that the shelter buffer of size 2 is large enough to handle most of the stagnation. If the shelter buffer of size 2 is employed, we can reduce the reorder buffer by 44% in Whetstone, 50% in FFT, 60% in FM, and 75% in Linpack benchmark program without loss of any throughput. Execution time is also improved by 19.78% in Whetstone, 19.67% in FFT, 23.93% in FM, and 8.65% in Linpack benchmark when the shelter buffer is used.