Improving the reliability of on-chip data caches under process variations

On-chip caches take a large portion of the chip area. They are much more vulnerable to parameter variation than smaller units. As leakage current becomes a significant component of the total power consumption, the leakage current variations induced thermal and reliability problem to the on-chip caches become an important design concern. This paper studies the impact of process variations, particular the leakage variations, on the temperature and reliability of on-chip caches. Our statistical simulation shows that, under process variation, 85% of the caches see shortened lifetime, with average lifetime being 81.6% of the ideal cache. At runtime, unevenly distributed dynamic power and the corresponding thermal variation would further deteriorate the situation. To mitigate this problem, we propose a dynamic cache subarray permutation scheme that can alleviate the thermal stress on a high-leakage area to improve the reliability of the caches. Experiments on 17 Spec2k benchmarks show that our scheme can extend the cache lifetime by up to 20.3%, and reduce the peak temperature by 7 degrees on average and more on data-intensive applications.