Cuckoo directory: A scalable directory for many-core systems

Michael Ferdman, Pejman Lotfi-Kamran, Ken Balet, Babak Falsafi
2011 2011 IEEE 17th International Symposium on High Performance Computer Architecture  
Growing core counts have highlighted the need for scalable on-chip coherence mechanisms. The increase in the number of on-chip cores exposes the energy and area costs of scaling the directories. Duplicate-tagbased directories require highly associative structures that grow with core count, precluding scalability due to prohibitive power consumption. Sparse directories overcome the power barrier by reducing directory associativity, but require storage area over-provisioning to avoid high
more » ... tion rates. We propose the Cuckoo directory, a power-and area-efficient scalable distributed directory. The cuckoo directory scales to high core counts without the energy costs of wide associative lookup and without gross capacity over-provisioning. Simulation of a 16-core CMP with commercial server and scientific workloads shows that the Cuckoo directory eliminates invalidations while being up to four times more powerefficient than the Duplicate-tag directory and 24% more power-efficient and up to seven times more areaefficient than the Sparse directory organization. Analytical projections indicate that the Cuckoo directory retains its energy and area benefits with increasing core count, efficiently scaling to at least 1024 cores.
doi:10.1109/hpca.2011.5749726 dblp:conf/hpca/FerdmanLBF11 fatcat:bzf3oskp5zheblfdh4oti64ir4