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IBM Blue Gene/Q memory subsystem with speculative execution and transactional memory

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8 Author(s)
Ohmacht, M. ; IBM Research Division, Thomas J. Watson Research Center, Yorktown Heights, NY, USA ; Wang, A. ; Gooding, T. ; Nathanson, B.
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The memory subsystem of the IBM Blue Gene®/Q Compute chip features multi-versioning and access conflict detection. Its ordered and unordered transaction modes implement both speculative execution (SE) and transactional memory (TM). Blue Gene/Q's large shared second-level cache serves as storage for speculative versions, allowing up to 30 MB of speculative state for the 64 threads of a Blue Gene/Q node, which in the extreme can be associated with a single large transaction. Using the shared access to speculative data, the SE model implements forwarding, allowing data produced by one thread to be accessed by another thread while both are still speculative. This paper presents an overview of Blue Gene/Q's approach to TM and SE: the memory subsystem hardware and operating system extensions, IBM XL compiler support via OpenMP® extensions, and a cost estimation model for executing code speculatively. The model is validated using synthetic benchmarks.

Note: The Institute of Electrical and Electronics Engineers, Incorporated is distributing this Article with permission of the International Business Machines Corporation (IBM) who is the exclusive owner. The recipient of this Article may not assign, sublicense, lease, rent or otherwise transfer, reproduce, prepare derivative works, publicly display or perform, or distribute the Article.  

Published in:

IBM Journal of Research and Development  (Volume:57 ,  Issue: 1/2 )