Optimizing Issue Queue Reliability to Soft Errors on Simultaneous Multithreaded Architectures

The issue queue (IQ) is a key microarchitecture structure for exploiting instruction-level and thread-level parallelism in dynamically scheduled simultaneous multithreaded (SMT) processors. However, exploiting more parallelism yields high susceptibility to transient faults on a conventional IQ. With the rapidly increasing soft error rates, the IQ is likely to be a reliability hot-spot on SMT processors fabricated with advanced technology nodes using smaller and denser transistors with lower threshold voltages and tighter noise margins. In this paper, we explore microarchitecture techniques to optimize IQ reliability to soft error on SMT architectures. We propose to use off-line instruction vulnerability profiling to identify reliability critical instructions. The gathered information is then used to guide reliability-aware instruction scheduling and resource allocation in multithreaded execution environments. We evaluate the efficiency of the proposed schemes across various SMT workload mixes. Extensive simulation results show that, on average, our microarchitecture level soft error mitigation techniques can significantly reduce IQ vulnerability by 42% with 1% performance improvement. To maintain runtime IQ reliability for pre-defined thresholds, we propose dynamic vulnerability management (DVM) mechanisms. Experimental results show that our DVM techniques can effectively achieve desired reliability/performance tradeoffs.