Dynamic adaptation of parallel codes Toward self-adaptable components for the Grid Françoise André, Jérémy Buisson & Jean-Louis Pazat

Principles of dynamic adaptation

• Modification of the executed code

• Reflexive programming

• Goal: better fit to allocated resources

Dynamic adaptation

• Three key questions:

• When should the component adapt?
• How should the component be modified?
• Where can the reaction be executed?

Dynamic adaptation

• When should the component adapt?

• Upon reception of an event from a monitor
• According to the policy

Dynamic adaptation

• How should the component be modified?

• Executing special code
• Following directives of the policy

Dynamic adaptation

• Where can the reaction be executed?

• At the next adaptation point
• Approximated prediction of the next point
• Based on control flow graph

Dynamic adaptation

Mixing parallelism and adaptation

Mixing parallelism and adaptation

• Introduction of global adaptation points

• All the processes at the same state
• Need to coordinate all the processes

• Example: SPMD code

• Adaptation point between each phase

Mixing parallelism and adaptation

• Need for a distributed algorithm for the parallel coordinator

• Only consider globally reachable points
• In the future of all the processes
• Make an agreement of all the processes
• Choose the same point for all the processes

Mixing parallelism and adaptation

• Need to control the non-determinism

• Due to parallelism
• Dynamically insert synchronization statements
• Due to unpredictable conditional instructions
• Force the result of the conditions if possible
• Example: insertion of empty iterations in loops
• Otherwise postpone the decision-making

Experiment

• Experiment

• Iterative SPMD code
• Adaptation points between each iteration
• Increase of the number of processors

• Results

• Negligible time in adaptation points
• Gain thanks to the adaptation
• Expected to scale well

Related domains

• Computation steering

• Notions equivalent to global adaptation points
• Need to execute some “special code” at the next “special point”
• Particular use of adaptation mechanisms
• User interface instead of monitors

Related domains

• Fault tolerance

• Consider dynamic environment
• Need for a global “consistent” state
• In the past for fault tolerance
• In the future for dynamic adaptation
• Relation to dynamic adaptation
• An application?
• A complementary feature?

Work done

• Design of the overall architecture

• Identification of functional “boxes”

• Distributed algorithm for the coordinator

• Automated instrumentation by static behavioral reification
• Simple negotiation protocol

• Demonstration prototype

• Ad-hoc mechanisms
• Proof of concept

Future work

• Generalizing the approach

• Generic definition of global adaptation points
• Limits of the “same state” definition
• Case of non-SPMD codes
• Expression of the adaptation policy
• Limits of explicit event-based rules
• Need for more sophisticated (intelligent?) policies
• Smoothing measures of resource availability
• Balancing instabilities

Future work

• Collaborative adaptation of components

• Control side-effects
• Avoid adaptation cycles
• Common policy at the level of:
• A group of components
• A composite
• The whole application
• Consider full Grid applications
• Not only their components

Dynamic adaptation of parallel codes Toward self-adaptable components for the Grid