Exploiting microarchitectural redundancy for defect tolerance

The continued increase in microprocessor clock frequency that has come from advancements in fabrication technology and reductions in feature size, creates challenges in maintaining both manufacturing yield rates and long-term reliability of devices. Methods based on defect detection and reduction may not offer a scalable solution due to cost of eliminating contaminants in the manufacturing process and increasing chip complexity. This paper proposes to use the inherent redundancy available in existing and future chip microarchitectures to improve yield and enable graceful performance degradation in fail-in-place systems. We introduce a new yield metric called performance averaged yield (Ypav) which accounts both for fully functional chips and those that exhibit some performance degradation. Our results indicate that at 250nm we are able to increase the Ypav of a uniprocessor with only redundant rows in its caches from a base value of 85% to 98% using microarchitectural redundancy. Given constant chip area, shrinking feature sizes increases fault susceptibility and reduces the base Ypav to 60% at 50nm, which exploiting microarchitectural redundancy then increases to 99.6%.