Achieving Predictable Performance in SMT Processors by Instruction Fetch Policy
With the applications in embedded systems increasingly complex, future embedded processors will resemble current high performance general purpose processors. Simultaneous multithreading (SMT) is a good choice in embedded processors for its good cost-performance trade-off. However, in SMT processors, the execute time of a thread is unpredictable. The unpredictability is an undesirable feature in embedded systems. In order to apply SMT architecture to embedded processors, the problem of performance unpredictability must be addressed. Among the current researches, a noted one is done by Cazorla et al (we call it Cazorla policy). However, Cazorla policy achieves predictable performance for a time critical thread by shared resources reservation, which weakens the advantage of resources sharing in SMT processors.
In this paper, we propose a novel instruction fetch policy called APP (Achieving Predictable Performance) to control the performance of a time critical thread in SMT processors. Simulation results show that APP can achieve predictable performance for the time critical thread as effectively as Cazorla policy does. Furthermore, APP can make full use of shared resources more effectively to optimize the performance of other co-scheduled threads and overall throughput. Compared with Cazorla policy, overall throughput obtained by APP is increased by 4.9% on average and the performance of other co-scheduled threads is increased by 17.6%.
KeywordsSimultaneous Multithreading Instruction Fetch Policy Predictable Performance
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