Are distributed sharing codes a solution to the scalability problem of coherence directories in manycores? An evaluation study.

Saved in:

Bibliographic Details
Title:	Are distributed sharing codes a solution to the scalability problem of coherence directories in manycores? An evaluation study.
Authors:	Fernández-Pascual, Ricardo¹ rfernandez@ditec.um.es, Ros, Alberto¹ aros@um.es, Acacio, Manuel¹ meacacio@um.es
Source:	Journal of Supercomputing. Feb2016, Vol. 72 Issue 2, p612-638. 27p.
Subjects:	Multiprocessors, Distributed shared memory, Distributed computing, Cache memory, Energy consumption
Abstract:	The development of efficient and scalable cache coherence protocols is a key aspect in the design of manycore chip multiprocessors. In this work, we present a comprehensive evaluation of a kind of cache coherence protocols that, despite having been already implemented during the 1990s for building large-scale commodity multiprocessors, have not been considered in the context of chip multiprocessors yet. In particular, we evaluate two directory-based cache coherence protocols based on the idea of having the sharing code of each memory block distributed between the different sharers (distributed sharing code). The first one employs simply-linked lists to encode the information about the sharers of the memory blocks, whilst the second one does the same using doubly-linked lists, which improves the management of replacements. We compare these two organizations with three protocols that use centralized sharing codes, each one having different directory memory overhead: one of them implementing a non-scalable bit-vector sharing code and the other two implementing more scalable limited-pointer schemes with one and two pointers, respectively. Simulation results show that for large-scale chip multiprocessors, the protocol based on distributed doubly-linked lists dramatically reduces the memory overhead of a non-scalable bit-vector directory, while at the same time it achieves its performance levels. This is achieved with just a small degradation on dynamic energy consumption (approximately 10 % on average). This way, our results point out that for manycores, coherence directories based on distributed sharing codes are appealing alternatives to contemporary coherence directories based on centralized sharing codes. [ABSTRACT FROM AUTHOR]
	Copyright of Journal of Supercomputing is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database:	Engineering Source

Description
Abstract:	The development of efficient and scalable cache coherence protocols is a key aspect in the design of manycore chip multiprocessors. In this work, we present a comprehensive evaluation of a kind of cache coherence protocols that, despite having been already implemented during the 1990s for building large-scale commodity multiprocessors, have not been considered in the context of chip multiprocessors yet. In particular, we evaluate two directory-based cache coherence protocols based on the idea of having the sharing code of each memory block distributed between the different sharers (distributed sharing code). The first one employs simply-linked lists to encode the information about the sharers of the memory blocks, whilst the second one does the same using doubly-linked lists, which improves the management of replacements. We compare these two organizations with three protocols that use centralized sharing codes, each one having different directory memory overhead: one of them implementing a non-scalable bit-vector sharing code and the other two implementing more scalable limited-pointer schemes with one and two pointers, respectively. Simulation results show that for large-scale chip multiprocessors, the protocol based on distributed doubly-linked lists dramatically reduces the memory overhead of a non-scalable bit-vector directory, while at the same time it achieves its performance levels. This is achieved with just a small degradation on dynamic energy consumption (approximately 10 % on average). This way, our results point out that for manycores, coherence directories based on distributed sharing codes are appealing alternatives to contemporary coherence directories based on centralized sharing codes. [ABSTRACT FROM AUTHOR]
ISSN:	09208542
DOI:	10.1007/s11227-015-1596-4