The Influence of Malloc Placement on TSX Hardware Transactional Memory

In this paper, we demonstrate the impact of the placement policies of memory allocators on the performance of applications that use hardware transactional memory. In particular, commonly used allocators such as the default GNUglib malloc allocator may place objects in such a way that causes hardware transactions to consistently abort, even when running single-threaded. In multithreaded applications, these consistent aborts can force applications to fall back to using locks, significantly limiting the parallelism. We also show that using index-aware allocators can avoid these pathological memory placements. We have observed read-only transactions commit where the ca che footprint exceeds the L2 size, but have never observed tr ansactions commit where the footprint is above the size of th e L3 with TSX-RTM, misses turn into aborts aborts : amplify impac t of misses; wasted cycles; loss of write-set from L1 aborts a lso force slow-path and loss of concurrent execution for TLE Thread-local problem shifts to global impediment Misses be come aborts become serialization