CSC 456 Fall 2013/4a bc

Load Balancing

In multi-processor systems, load-balancing is used to break-up and distribute the work load to individual processors in order to make effective use of processor time. When the work load is divided up at compile-time, the balance is said to be statically balanced. Dividing the work load up during run-time is dynamically balancing the load. Static load balancing has reduced overhead as the work is divided before run time. Dynamic load balancing assigns work as processors become idle, so there is greater overhead. However, dynamic balancing can lead to increased performance of load balancing due to being able to assign work to a processor when it does become idle, reducing the overall idle time of processors.

Examples of Load Balancing in action

Server Load balancing pseudocode

server_load_vec_desc = sort_descending(server_load_vec);
server_load_vec_asc = sort_ascending(server_load_vec);
while (server_load_vec_desc[0].deviation > DEVIATION_THRESHOLD) {
  populate_range_load_vector(server_load_vec_desc[0].server_name);
  sort descending range_load_vec;
  i=0;
  while (server_load_vec_desc[0].deviation > DEVIATION_THRESHOLD &&
            i < range_load_vec.size()) {
    if (moving range_load_vec[i] from server_load_vec_desc[0] to server_load_vec_asc[0] reduces deviation) {
       add range_load_vec[i] to balance plan
       partial_deviation = range_load_vec[i].loadestimate * loadavg_per_loadestimate;
       server_load_vec_desc[0].loadavg -= partial_deviation;
       server_load_vec_desc[0].deviation -= partial_deviation;
       server_load_vec_asc[0].loadavg += partial_deviation;
       server_load_vec_asc[0].deviation += partial_deviation;
       server_load_vec_asc = sort_ascending(server_load_vec_asc); 
    }
    i++;
  }
  if (i == range_load_vec.size())
    remove server_load_vec_desc[0] and corresponding entry in server_load_vec_asc  
  server_load_vec_desc = sort_descending(server_load_vec_desc);
}




Sources

1. Load Balancing PseudoCode and other information