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Impact of L1 entire locking and L2 way locking on the performance, power consumption, and predictability of multicore real-time systems

Based on the recent design trend from giant chip-vendors, multicore systems are being deployed with multilevel caches to achieve higher levels of performance. Supporting real-time applications on multicore systems becomes a great challenge as caches are power hungry and caches make the execution time predictability worse. Studies show that timing predictability can be improved using cache locking techniques. However, level-1 (L1) entire locking may not be efficient if smaller amount of instructions/data compared to the cache size is locked. An alternative choice may be way locking. For some processors, way locking is possible at level-2 (L2) cache (not permitted at L1). Even though both L1 entire locking and L2 way locking improve predictability, it is difficult to justify the performance and power trade-off between these two locking mechanisms. In this work, we simulate a multicore system with two levels of caches to explore the impact of L1 entire locking and L2 way locking on the performance, power consumption, and predictability. Simulation results using FFT, DFT, and MPEG4 algorithms show that both performance and predictability can be increased and power consumption can be decreased by using a cache locking mechanism added to a cache memory hierarchy. Results also show that for FFT and DFT, L2 way locking outperforms L1 entire locking; but for MPEG4, L1 entire locking performs better than L2 way locking.