Accurate branch prediction for short threads

13 years 6 months ago

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Multi-core processors, with low communication costs and high availability of execution cores, will increase the use of execution and compilation models that use short threads to expose parallelism. Current branch predictors seek to incorporate large amounts of control flow history to maximize accuracy. However, when that history is absent the predictor fails to work as intended. Thus, modern predictors are almost useless for threads below a certain length. Using a Speculative Multithreaded (SpMT) architecture as an example of a system which generates shorter threads, this work examines techniques to improve branch prediction accuracy when a new thread begins to execute on a different core. This paper proposes a minor change to the branch predictor that gives virtually the same performance on short threads as an idealized predictor that incorporates unknowable pre-history of a spawned speculative thread. At the same time, strong performance on long threads is preserved. The proposed te...

Bumyong Choi, Leo Porter, Dean M. Tullsen

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