NDLI: LiteTM: Reducing transactional state overhead

Content Provider	IEEE Xplore Digital Library
Author	Jafri, S.A.R. Thottethodi, M. Vijaykumar, T.N.
Copyright Year	2010
Description	Author affiliation: School of Electrical and Computer Engineering, Purdue University (Jafri, S.A.R.; Thottethodi, M.; Vijaykumar, T.N.)
Abstract	Transactional memory (TM) has been proposed to address some of the programmability issues of chip multiprocessors. Hardware implementations of transactional memory (HTMs) have made significant progress in providing support for features such as long transactions that spill out of the cache, and context switches, page and thread migration in the middle of transactions. While essential for the adoption of HTMs in real products, supporting these features has resulted in significant state overhead. For instance, TokenTM adds at least 16 bits per block in the caches which is significant in absolute terms, and steals 16 of 64 (25%) memory ECC bits per block, weakening error protection. Also, the state bits nearly double the tag array size. These significant and practical concerns may impede the adoption of HTMs, squandering the progress achieved by HTMs. The overhead comes from tracking the thread identifier and the transactional read-sharer count at the L1-block granularity. The thread identifier is used to identify the transaction, if only one, to which an L1-evicted block belongs. The read-sharer count is used to identify conflicts involving multiple readers (i.e., write to a block with non-zero count). To reduce this overhead, we observe that the thread identifiers and read-sharer counts are not needed in a majority of cases. (1) Repeated misses to the same blocks are rare within a transaction (i.e., locality holds). (2) Transactional read-shared blocks that both are evicted from multiple sharers' L1s and are involved in conflicts are rare. Exploiting these observations, we propose a novel HTM, called LiteTM, which completely eliminates the count and identifier and uses software to infer the lost information. Using simulations of the STAMP benchmarks running on 8 cores, we show that LiteTM reduces TokenTM's state overhead by about 87% while performing within 4%, on average, and 10%, in the worst case, of To ke nTM.
Starting Page	1
Ending Page	12
File Size	407627
Page Count	12
File Format	PDF
ISBN	9781424456581
ISSN	15300897
e-ISBN	9781424456598
DOI	10.1109/HPCA.2010.5416653
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2010-01-09
Publisher Place	India
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Hardware Switches Parallel programming Delay Error correction codes Protection Impedance Power dissipation System recovery
Content Type	Text
Resource Type	Article

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