Partitioning and Communication

• Need to reduce inherent communication
  • This is the part of communication determined by assignment of tasks
  • There may be other communication traffic also (more later)
• Goal is to assign tasks such that accessed data are mostly local to a process
  • Ideally I do not want any communication
  • But in life sometimes you need to talk to people to get some work done!

Domain Decomposition

• Normally applications show a local bias on data usage
  • Communication is short-range e.g. nearest neighbor
  • Even if it is long-range it falls off with distance
  • View the dataset of an application as the domain of the problem e.g., the 2-D grid in equation solver
  • If you consider a point in this domain, in most of the applications it turns out that this point depends on points that are close by
  • Partitioning can exploit this property by assigning contiguous pieces of data to each process
  • Exact shape of decomposed domain depends on the application and load balancing requirements