Adopting the Drowsy Technique for Instruction Caches: A Soft Error Perspective

Soong Hyun SHIN  Sung Woo CHUNG  Eui-Young CHUNG  Chu Shik JHON  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E91-A   No.7   pp.1772-1779
Publication Date: 2008/07/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e91-a.7.1772
Print ISSN: 0916-8508
Type of Manuscript: PAPER
Category: VLSI Design Technology and CAD
instruction cache,  soft error,  drowsy technique,  low-power,  

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As technology scales down, leakage energy accounts for a greater proportion of total energy. Applying the drowsy technique to a cache, is regarded as one of the most efficient techniques for reducing leakage energy. However, it increases the Soft Error Rate (SER), thus, many researchers doubt the reliability of the drowsy technique. In this paper, we show several reasons why the instruction cache can adopt the drowsy technique without reliability problems. First, an instruction cache always stores read-only data, leading to soft error recovery by re-fetching the instructions from lower level memory. Second, the effect of the re-fetching caused by soft errors on performance is negligible. Additionally, a considerable percentage of soft errors can occur without harming the performance. Lastly, unrecoverable soft errors can be controlled by the scrubbing method. The simulation results show that the drowsy instruction cache rarely increases the rate of unrecoverable errors and negligibly degrades the performance.