An Aging-Aware GPU Register File Design Based on Data Redundancy

Nowadays, GPUs sit at the forefront of high-performance computing thanks to their massive computational capabilities. Internally, thousands of functional units, architected to be fed by large register files, fuel such a performance. At deep nanometer technologies, the SRAM memory cells that implement GPU register files are very sensitive to the Negative Bias Temperature Instability (NBTI) effect. NBTI ages cell transistors by degrading their threshold voltage $V_{th}$ over the lifetime of the GPU. This degradation, which manifests when a cell keeps the same logic value for a relatively long period of time, compromises the cell read stability and increases the transistor switching delay, which can lead to wrong read values and eventually exceed the processor cycle time, respectively, so resulting in faulty operation. This work proposes architectural mechanisms leveraging the redundancy of the data stored in GPU register files to attack NBTI aging. The proposed mechanisms are based on data compression, power gating, and register address rotation techniques. All these mechanisms working together balance the distribution of logic values stored in the cells along the execution time, reducing both the overall $V_{th}$ degradation and the increase in the transistor switching delays. Experimental results show that a conventional GPU register file suffers the worst case for NBTI, since a significant fraction of the cells maintain the same logic value during the entire application execution (i.e., a 100 percent ‘0’ and ‘1’ duty cycle distributions). On average, the proposal reduces these distributions by 58 and 68 percent, respectively, which translates into $V_{th}$ degradation savings by 54 and 62 percent, respectively.