Reducing NBTI-induced processor wearout by exploiting the timing slack of instructions

Transistor aging due to Negative Bias Temperature Instability (NBTI) is a major reliability challenge for embedded microprocessors at nanoscale. It leads to increasing path delays and eventually more failures during runtime. In this paper, we propose a novel microarchitectural approach combining aging-aware instruction scheduling with specialized functional units to alleviate the impact of NBTI-induced wearout. To achieve this, the instructions are classified depending on their worst-case delay into critical (i.e. the instructions whose delay is close to the cycle boundary) and non-critical instructions (i.e. those instruction with larger timing slack). Each of these classes uses its own (specialized) functional unit(s). By that means it is possible to increase the idle ratio of the units executing the critical instructions, which can be used to extend lifetime by up to 2.3x in average compared to the usually used balanced scheduling policy.