Analysis and solutions to issue queue process variation

The last few years have witnessed an unprecedented explosion in transistor densities. Diminutive feature sizes have enabled microprocessor designers to break the billion-transistors per chip mark. However various new reliability challenges such as Process Variation (PV) have emerged that can no longer be ignored by chip designers. In this paper, we provide a comprehensive analysis of the effects of PV on the microprocessor's Issue Queue. Variations can slow down issue queue entries and result in as much as 20.5% performance degradation. To counter this, we look at different solutions that include Instruction Steering, Operand- and Port- switching mechanisms. Given that PV is non-deterministic at design-time, our mechanisms allow the fast and slow issue-queue entries to co-exist in turn enabling instruction dispatch, issue and forwarding to proceed with minimal stalls. Evaluation on a detailed simulation environment indicates that the proposed mechanisms can reduce performance degradation due to PV to a low 1.3%.