Approximate Lock: Trading off Accuracy for Performance by Skipping Critical Sections

Approximate computing is gaining a lot of traction due to its potential for improving performance and consequently, energy efficiency. This project explores the potential for approximating locks. We start out with the observation that many applications can tolerate occasional skipping of computations done inside a critical section protected by a lock. This means that for certain critical sections, when the enclosed computation is occasionally skipped, the application suffers from quality degradation in the final outcome but it never crashes/deadlocks. To exploit this opportunity, we propose Approximate Lock (ALock). The thread executing ALock checks if a certain condition (e.g., high contention, long waiting time) is met and if so, the thread returns without acquiring the lock. We modify some selected critical sections using ALock so that those sections are skipped when ALock returns without acquiring the lock. We experimented with 14 programs from PARSEC, SPLASH2, and STAMP benchmarks. We found a total of 37 locks that can be transformed into ALock. ALock provides performance improvement for 10 applications, ranging from 1.8% to 164.4%, with at least 80% accuracy.