NBTI mitigation by optimized NOP assignment and insertion

Negative Bias Temperature Instability (NBTI) is a major source of transistor aging in scaled CMOS, resulting in slower devices and shorter lifetime. NBTI is strongly dependent on the input vector. Moreover, a considerable fraction of execution time of an application is spent to execute NOP (No Operation) instructions. Based on these observations, we present a novel NOP assignment to minimize NBTI effect, i.e. maximum NBTI relaxation, on the processors. Our analysis shows that NBTI degradation is more impacted by the source operands rather than instruction opcodes. Given this, we obtain the instruction, along with the operands, with minimal NBTI degradation, to be used as NOP. We also proposed two methods, software-based and hardware-based, to replace the original NOP with this maximum aging reduction NOP. Experimental results based on SPEC2000 applications running on a MIPS processor show that this method can extend the lifetime by 37% in average while the overhead is negligible.