Cooperatively managing dynamic writeback and insertion policies in a last-level DRAM cache

Stacked-DRAM used as the last-level caches(LLC) in multi-core systems delivers performance enhancement due to its capacity benefit. While the performance of LLC depends heavily upon its block replacement policy, conventional replacement policy needs redesigning to exploit the best of DRAM cache while avoiding its drawbacks. Existing DRAM cache insertion policy blindly forwards victim lines to the off-chip memory, regardless of the potential for increased hits by placing a fraction of them in the DRAM cache; nevertheless, a na¨ıve design that steers all dirty victims to the DRAM cache introduces excessive writeback traffic which aggravates capacity misses and DRAM interference. To leverage insertions in terms of writeback or fill requests, we propose a cooperative writeback and insertion policy that adapts to the distinct access patterns of heterogeneous applications based on runtime misses and writeback efficiency, thereby increasing HMIPC (harmonic instruction per cycle) throughput by 22.2%, 13.7% and 14.5% compared to LRU and two static writeback policies.