Manel velasco and pau mart universitat polit cnica de catalunya manel velasco pau marti @upc edu
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Manel Velasco and Pau Martí Universitat Politècnica de Catalunya {manel.velasco,[email protected] 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 mart universitat polit cnica de catalunya manel velasco pau marti @upc edu l.jpg

Manel Velasco and Pau MartíUniversitat Politècnica de Catalunya{manel.velasco,[email protected]

Adaptivity through event-driven systems

resource management

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


Development framework l.jpg
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


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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


General loop diagram l.jpg
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


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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


Layered structure6 l.jpg
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


Adaptivity seen as resource management l.jpg
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


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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


Adaptivity free as much resources as possible l.jpg
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


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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


Adaptivity the event driven control l.jpg
Adaptivity: The Event-Driven Control

How it works:

From an initial state you set a boundary and a control action

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x

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s

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


Adaptivity the event driven control12 l.jpg
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


Adaptivity the event driven control13 l.jpg
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

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


Adaptivity the event driven control14 l.jpg
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

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e2

e1

s

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


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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


Adaptivity the event driven control16 l.jpg
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


Adaptivity the event driven control17 l.jpg
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


Adaptivity the event driven control18 l.jpg
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

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


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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


Example l.jpg
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


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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


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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


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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


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


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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


Adaptivity free as much resources as possible26 l.jpg
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


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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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