BulkCompactor: Optimized deterministic execution via Conflict-Aware commit of atomic blocks

Abstract

Recent proposals for determinism-enforcement architectures are able to honor the dependences between threads through a commit step that often becomes a performance bottleneck. As they commit code blocks (or chunks) in a round-robin order, if one chunk gets squashed due to a conflict, its successors also observe a stall. We call this effect transitive squash delay.This paper proposes a novel, high-performance approach to deterministic execution based on Conflict-Aware commit. Rather than committing chunks in strict round-robin order, the idea is to skip those chunks with conflicts and deterministically execute them slightly later. The scheme, called BulkCompactor, largely eliminates transitive squash delay, "compacts" the chunk commits, and substantially speeds-up execution. With BulkCompactor, the squash overhead is O(N ) rather than O(N 2 ) as in round-robin. We describe BulkCompactor designs for machines with centralized or distributed commit. Finally, a simulation-based evaluation shows that BulkCompactor delivers performance comparable to nondeterministic systems. For example, for 32 processors, BulkCompactor incurs an average execution overhead of 22% over a nondeterministic system. The round-robin scheme's average overhead is 133%.

Extending the applicability of deterministic multithreading

“…BulkCompactor (Duan et al [28]) is a deterministic system implemented in hardware with the improved order of chunk (quantum) execution in comparison to the traditional round-robin order. The chunks that have to be re-executed due to conicts are skipped, and they are re-executed in the next round of token passing.…”