Summary: Directory-Based Conflict Detection in
Hardware Transactional Memory
Rub´en Titos, Manuel E. Acacio, and Jos´e M. Garc´ia
Departamento de Ingenier´ia y Tecnolog´ia de Computadores
Universidad de Murcia, 30100 Murcia (Spain)
Abstract. One of the key design points of any hardware transactional
memory (HTM) system is the conflict detection mechanism, and its effi-
cient implementation becomes critical when conflicts are not a rare event.
While many contemporary proposals rely on the coherence protocol to
carry out conflict detection at the private cache levels, this approach
is not optimal for systems that use a directory to maintain coherence
over an unordered, scalable network, such as tiled CMPs. In this paper,
we present a new scheme of conflict detection for HTM systems, which
moves this key mechanism from the private caches to the directory level.
We propose a novel transactional book-keeping method and describe how
this detection can be carried out more efficiently at the directory. Simula-
tion results show that our approach obtains reductions in execution time
between 25 and 55% for transactional benchmarks with a high number
of conflicts, with an average improvement over LogTM-SE of 15%.