Thread-Level Transactional Memory

This paper presents thread-level transactional memory (TTM), a memory system interface that separates the semantics of transactions—atomicity, consistency, and isolation—from the implementation. By making transactions a thread-level abstraction, TTM permits implementations using different combinations of of high-level software, low-level software, and dedicated hardware. TTM tracks a transaction’s read and write sets and creates a "before-image" log in the thread’s virtual address space. We evaluate four TTM implementations—broadcast and directory coherence times two different transaction abort mechanisms—using full-system simulation. Like previous transactional memory systems, TTM implementations are competitive with or better than lock-based synchronization. TTM’s ability to cache the before and after images both supports large transactions and enables low memory bandwidth on successful commits and fast rollback on aborts.