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Amdahl's Law in the Multicore Era

April 7, 2009
Time: 2:00 PM
Location: NSEC 220

Mark D. Hill
Computer Sciences Department
University of Wisconsin-Madison
http://www.cs.wisc.edu/~markhill/

Over the last several decades computer architects have been phenomenally successful turning the transistor bounty provided by Moore's Law into chips with ever increasing single-threaded performance. During many of these successful years, however, many researchers paid scant attention to multiprocessor work. Now as vendors turn to multicore chips, researchers are reacting with more papers on multi-threaded systems. While this is good, we are concerned that further work on single-thread performance will be squashed. To help understand future high-level trade-offs, we develop a corollary to Amdahl's Law for multicore chips [Hill & Marty, IEEE Computer 2008]. It models fixed chip resources for alternative designs that use symmetric cores, asymmetric cores, or dynamic techniques that allow cores to work together on sequential execution. Our results encourage multicore designers to view performance of the entire chip rather than focus on core efficiencies. Moreover, we observe that obtaining optimal multicore performance requires further research BOTH in extracting more parallelism and making sequential cores faster. This talk is based on an HPCA 2008 keynote address.



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