Montek Singh COMP Oct 11, 2011
Basics of multicore systems ◦ what is multicore? ◦ why multicore? ◦ main features ◦ examples Next two classes ◦ case studies ◦ benefits and challenges ◦ key research problems
Two or more CPU cores on a single die ◦ typically share L2 cache ◦ typically separate L1 caches ◦ share main memory
What was happening before c. 2010? What started happening c. 2010? Why?
Three main technological reasons ◦ Memory Wall increasing gap between CPU and memory speeds no longer makes sense to simply make CPU faster ◦ ILP Wall increasing difficulty in finding enough parallelism in single stream of instructions tried hyper-threading already ◦ Power Wall increasing frequency was increasing power density without so much increase in performance poses big manufacturing problems
Main manufacturing advantages over discrete processors ◦ on-chip caches faster shared L2 cache ◦ physical proximity of CPUs allows cache coherence circuitry to be much faster ◦ inter CPU communication much faster than traditional multiprocessor supercomputers ◦ much less PCB area than discrete processors ◦ higher performance/power ratio voltage scaling
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