SUV: A Novel Single-Update Version-Management Scheme for Hardware Transactional Memory Systems

In order to maintain the transactional semantics, Transactional Memory (TM) must guarantee isolated read and write operations in each transaction, meaning that it must spend a non-negligible and potentially significant amount of time on keeping track of the transactional modifications in its undo or redo log and switching to the proper version at the end of each transaction. Existing TMs failed to minimize the overheads incurred by these operations that are poised to impose more significant TM overheads in current and future many-core CMPs. A direct consequence of this is that extra and different data movements are needed to manage these modifications depending on commit or abort. To address this problem, we propose a novel Single-Update Version-management (SUV) scheme to redirect each transactional store operation to another memory address, track the mapping information between the original and redirected addresses, and switch to the proper version of data upon the transaction´s commit or abort. There is only one data update (movement) in our SUV regardless of commit or abort, thus significantly reducing the TM overheads while allowing it to exploit more thread parallelism. We use SUV to replace version-management schemes in some existing hardware TMs to assess SUV´s performance advantages. Our extensive execution-driven experiments show that SUV-TM consistently outperforms the state-of-the-art HTM schemes Log TM-SE, FasTM and DynTM under the STAMP benchmark suite. Moreover, we use CACTI to estimate the hardware overheads of SUV and find it is feasible in hardware implementation.