Asymmetric Allocation in a Shared Flexible Signature Module for Multicore Processors

Hardware signatures based on Bloom filters are used to support and accelerate membership query in a set of items. They use modest hardware at the cost of false positives, but never produce false negatives. Signatures were traditionally used in different distributed and network applications, but in recent years their use has been extended to other fields (for instance, support for manycore/multicore parallel programming, such as data race detection, deterministic replay or transactional memory (TM)). One drawback of signatures is that they have a fixed size, and what is a good signature size for one application, may be not appropriate for another. Recently, we proposed a shared hardware module for managing signatures based on a collection of Bloom filters. It has the characteristic of hosting a variable number of signatures that change their size in runtime to adapt to the demand of the applications. However, the assignment of resources follows a single symmetric policy for all allocations leading to a module with a limited adaptability to the workloads. In this paper, we explore new techniques to allocate signatures in an asymmetric way in this module, with the aim of optimizing the resources and reducing even more the number of false positives. We explore several asymmetric strategies and their efficient hardware implementation, and we show specific examples using TM as a driver application. The results show that these strategies lead to a significant reduction in the number of false positives compared with symmetric policies.