LogTM: Log-based Transactional Memory

Overview

We introduced Log-Based Transactional Memory (LogTM) at HPCA (2/2006) and extended it to support nested transactions at ASPLOS (10/2006). LogTM differs from most other transactional memory systems primarily in that transactional stores eagerly update memory "in place" while recording old values in a per-thread log. Common-case transactional commits are fast, because data is in place and need not move. Less common transactional aborts, however, use software handlers to restore old values from the log. LogTM's transaction log and software aborts extend naturally to nested transactions. Each nested transaction allocates its own frame on log much like a function call pushes an activation record on the stack. Software abort processing cleanly supports unrolling arbitrary nesting levels and allows the execution of compensating actions without additional hardware.

LogTM-Signature Edition replaced transactional bits in the cache with a signature that supports virtualization. With signatures, which may be saved and restored in software, transactions can exceed the cache size, and surivive both context switches and virtual memory paging.

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