Instruction-set extension under process variation and aging effects

We propose a novel custom instruction (CI) selection technique for process variation and transistor aging aware instruction-set architecture synthesis. For aggressive clocking, we select CIs based on statistical static timing analysis (SSTA), which achieves efficient speedup during target lifetime while mitigating degradation of timing yield (i.e., probability of satisfying the timing). Furthermore, we consider process variation and aging on not only CIs but also basic instructions (BIs). Even if basic functional units (BFUs), e.g., ALU, get slower due to aging, only a few BIs with critical propagation delay may violate the timing, whereas the other BIs running on the same BFU can still satisfy the timing. We then introduce "customized BFUs", which execute only such aging-critical BIs. The customized BFUs, used as spare BFUs of the aging-critical BIs, can extend lifetime of the system. Combining the two approaches enables speedup as well as lifetime extension with no or negligibly small area/power overhead. Experiments demonstrate that our work outperforms conventional worst-case work (by an average speedup of about 49%) and existing SSTA-based work (16x or more lifetime extension with comparable speedup).