1. Montek Singh COMP790-084 Oct 11, 2011

2.  Basics of multicore systems ◦ what is multicore? ◦ why multicore? ◦ main features ◦ examples  Next two classes ◦ case studies ◦ benefits and challenges ◦ key research problems

3.  Two or more CPU cores on a single die ◦ typically share L2 cache ◦ typically separate L1 caches ◦ share main memory

4.  What was happening before c. 2010?  What started happening c. 2010?  Why?

5.  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

7.  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

8.  Frontside and Backside buses  Northbridge and Southbridge