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Manel Velasco and Pau Martí Universitat Politècnica de Catalunya {manel.velasco,pau.marti}@upc

Manel Velasco and Pau Martí Universitat Politècnica de Catalunya {manel.velasco,pau.marti}@upc.edu. Adaptivity through event-driven systems resource management . Development Framework. System model: N control tasks simultaneously running on top of a resource-constrained computing system

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Manel Velasco and Pau Martí Universitat Politècnica de Catalunya {manel.velasco,pau.marti}@upc

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  1. Manel Velasco and Pau MartíUniversitat Politècnica de Catalunya{manel.velasco,pau.marti}@upc.edu Adaptivity through event-driven systems resource management ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  2. Development Framework System model: N control tasks simultaneously running on top of a resource-constrained computing system Picture ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  3. Development Framework Objectives (adaptivity): • Adaptivity driven by specifications on the application: • Redistribute resources among control tasks to meet performance specifications. • Adaptivity driven by specifications on the computing platform: • Keep target performance while using as less resources as possible Key mechanism: Sampling period: relates control performance and resource usage Tools: Optimal off-line assignment Mixed off-line on-line assignment Feedback scheduling … Event-driven control (emerging… but not new) ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  4. General loop diagram Double control loop model: Outer control loop that adapts the resource utilization of each task taking into account the overall resource usage and the state of the application driven by each task Inner control loop is able to adapt to the new scenario Set-point ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  5. Layered structure Just before going on…: Who is going to deal with the upper layer feedback? Who makes the upper feedback operation? Set-point Action Action Action Action? Measurement? Control loops ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  6. Layered structure Just before going on…: Who is going to deal with the upper layer feedback? Who makes the upper feedback operation? Set-point Action Action Action System? Measurement? Control loops ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  7. Adaptivity seen as resource management Maximize aggregated control loop performance by fully and cleverly exploiting the available resources There are many works on FS. All them are able to adapt task periods to meet the imposed constrains. BUT… Control tasks are passive respect to resource usage. The model may present critical delays. Feedback scheduling (FS) ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  8. Real-time control adaptivity? Some considerations: Resources should be available when they are needed. When will I need them?... Adapting to some resource usage level “in time” (meta-real-time?) may be important. Delays in adaptation may cause oscillations!!!, there is a complete dynamical system behind resources management which has to be identified and controlled. Right now we are working around the easiest solution: Free as much resources as possible to allow any task to use them when needed ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  9. Adaptivity: free as much resources as possible Minimize resource utilization while keeping some target performance: Not a new idea (from the 50s), but receiving renewed attention lately. What can be done to reduce resource usage?: To avoid computations if the system is evolving in the “right direction” From a theoretical point of view, and if no perturbation acts on the system, once you get to the equilibrium point you are finished. Event-driven control Also known as adaptive sampling, Lebesgue sampling, self-triggered sampling Key idea: Use resources only when it is mandatory ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  10. Adaptivity: free resources as soon as possible Minimize resource utilization while keeping some target performance Event-driven control Key idea: Use resources only when it is mandatory Key question: when is it mandatory? ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  11. Adaptivity: The Event-Driven Control How it works: From an initial state you set a boundary and a control action abs(x) s x k s ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  12. Adaptivity: The Event-Driven Control How it works: From an initial state you set a boundary and a control action The system evolves as itis expected by its equations abs(x) s x k s ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  13. Adaptivity: The Event-Driven Control How it works: From an initial state you set a boundary and a control action The system evolves as itis expected by its equations Once the boundary is reached a new controlaction is computed and also a new boundary S y s t em t r aje c t o r y abs(x) s e x k s ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  14. Adaptivity: The Event-Driven Control How it works: From an initial state you set a boundary and a control action The system evolves as itis expected by its equations Once the boundary is reached a new controlaction is computed and also a new boundary The final result is an acceptableperformance with less resourceusage e4 e3 s e2 e1 s ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  15. Adaptivity: The Event-Driven Control Which is the difference between time-driven control and event-driven control? Both use a boundarys, one is set up in time and the second is set in the space. Depending on how you design the boundary you may save some resources. ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  16. Adaptivity: The Event-Driven Control Which is the difference between time-driven control and event-driven control? Both use a boundary, one is set up in time and the second is set in the space. Depending on how you design the boundary you may save some resources. ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  17. Adaptivity: The Event-Driven Control Which is the difference between time-driven control and event-driven control? Both use a boundary, one is set up in time and the second is set in the space. Depending on how you design the boundary you may save some resources. ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  18. Adaptivity: The Event-Driven Control Where is the adaptation here? If you change the boundary size or shape you get different resource usage, and different sampling patterns e 4 e 3 e 4 e 3 s e 2 e s 2 e s 1 e s 1 ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  19. Adaptivity: Modeling issues Controller model Boundary description: e.g. Intersample time: recursivity between ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  20. Example: System controlled: Ball & Beam Methods used: Event-driven & Time-driven Controller: Same gains for both Performance: Same performance (approx.) Periods: Event-driven Time-driven 0.4 0.2 0 0 2 4 6 8 10 12 Results: We save resources while ensuring control performance The sampling “period” is oscillating !! This forces the rest of tasks to adapt to our needs This kind of control does not take into account the processor's load ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  21. Adaptivity: Modeling issues We are working on a system model that includes as state variable the processor's load produced by its own execution… self-scheduling? Once we have the model it is possible to control it, allowing (self) adaptivity to application, computing platform and/or environment demands It is not a new idea, six years ago it was presented the Self-triggered task model, but now we have more deep knowledge on how it works. ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  22. Adaptivity: Upper levels May we apply these ideas to some other areas? Control of computing systems… Example: Event-driven scheduling Feedback scheduling Task 2 Push action Task 1 ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  23. Conclusions & Future work Conclusions: Right now, adaptivity is a never end list of questions In control theory (also in other areas) there is some work done around this problem There are basic problems unsolved from a control point of view (dynamical models of whatever you want to control) Future work: Event-driven control is an old but re-emerging discipline that can help on adaptivity. Tasks, and in our specific area control tasks, should be aware of some system data. Having this data we may use some collaborative technique to allow self-adaptivity There is a lot of work to be done ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  24. ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  25. Adaptivity: Modeling issues Extending the intersampling system’s state With the solution of the sampling interval ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  26. Adaptivity: free as much resources as possible Minimize resource utilization while keeping some target performance Event-driven control Key idea: Use resources only when it is mandatory ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

  27. If we are on this slide, then it’s dinner time. Are you hungry? ArtistDesign Workshop on Design for Adaptivity May 13-14, 2008       Lund, Sweden

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