Module 5: Performance Issues in Shared Memory and Introduction to Coherence
Lecture 10: Introduction to Coherence
Four Organizations
Dancehall
Better scalability compared to previous two designs
The difference from bus-based SMP is that the interconnect is a scalable point-to-point network (e.g. crossbar or other topology)
Memory is still symmetric from all processors
Drawback:
a cache miss may take a long time since all memory banks too far off from the processors (may be several network hops)
Distributed shared memory
The most popular scalable organization
Each node now has local memory banks
Shared memory on other nodes must be accessed over the network
Remote memory access
Non-uniform memory access (NUMA)
Latency to access local memory is much smaller compared to remote memory
Caching is very important to reduce remote memory access
