Charms Migration Capabilities

1
Charms Migration Capabilities

• Extensive set of tools for moving pieces of a
  computation between processors
• Isomalloc thread stacks for migratable threads
• Isomalloc heaps to avoid special move code (pup
  routine)
• Challenging to get right!
• Can rebalance when application changes
• Mesh coarsening/refinement
• Changing physics solvers
• Changing communication patterns
• Can respond to changes in the machine
• Expand running computation to newly available
  processors
• Shift running computation away from timeshared
  processors

2
Thread Migration Example

• In Rocfrac, Processor 1 has too much work

• Load balancer moves some work to processor 0
• One AMPI process, or virtual processor
• Rocfrac speeds up by 30
• Time per step shrinks from 90ms to 60ms