Early Execution for Soft Error Detection

Single event upsets have made modern integrated circuits more susceptible to soft errors, making their operation less reliable. In order to detect induced computational faults, we propose a fault-tolerant, low-overhead microarchitecture that detects soft errors using temporal redundancy. The idea of introducing an Early Execution Unit (EXU) at the processor frontend has been explored by previous proposals in order to execute dynamic instructions with short dependency chains expeditiously for performance improvement. However, we observe that the functional units in the EXU are idle for a significant portion of the program execution duration. Our proposed microarchitecture utilises these inactive frontend functional units in order to re-execute dynamic instructions to ascertain computational correctness. A low-overhead backend verifier leverages idle resources for redundant execution using the proposed priority-based scheduling algorithm that interleaves program execution with re-execution for error detection. Our proposal provides exhaustive transient fault coverage while improving performance by 7.5% over an existing restricted OoO microarchitecture, Freeflow Core, delivering IPC close to that of an out-of-order baseline, while being $1.78 \times $ more energy-efficient than the involuted, power-hungry out-of-order design.