Control Theoretical Model for QoS Adaptations

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15 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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Control Theoretical Model for QoS Adaptations

Goal: develop a Task Control Model to formally model
applications that adapt to resource/QoS variations

Use digital control theory

Analyze equilibrium, stability and fairness

Model realistic cases where complete task state
information are not observable

Map to an adaptive control system


Target System

to be controlled takes actions to process


input is determined by a


controller monitors states or output of target system and
compares them to desired values (the

Task Flow Model

Consider each application as an ensemble of functional
components (

A task performs certain actions to deliver a result to
other tasks or end

Task Flow Graph is a directed acyclic graph showing
dependencies among tasks

A task can be uniquely characterized by its input
quality, output quality and utilized resources (needed
to perform actions)

Task Control Model

Models a single task in the Task Flow Graph

This is the
Target Task

to be controlled

In addition,


Adaptation Task

performs the adaptive control


Observation Task

observes states of the Target Task
and feeds them back to Adaptation Task

Task Control Model (cont’d)

Adaptation Task modifies a set of


possible to affect their values, which
in turn can affect states of Target Task and thus its
output quality

Task States characterize the internal dynamics in the
Target Task. The most important states are its
parameters related to its resources

Observation Task observes task states if they are
. If not, estimates or predicts the current

Control Equations

Task is said to be at

when its state
does not change

Assume Target Task can be characterized accurately
by discrete
time equations


Resource requests for temporal or spatial resources

Request rate of a task throttled by Adaptation Task,
so that it does not exceed its fair share

Assume to observe the

number of outstanding
resource requests made by

tasks at time k

Under PID control, find stability conditions,
equilibrium states, and evaluate responsiveness

Show stability, equilibrium and configurability are
preserved when Observation Task can only observe
the number of outstanding requests made by the task