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consists of the implementation of the
uses
function. Such implementation resides
in a separate component, that takes as input (also) the asserted constraints on the
platform. Those constraints come from the software applications, and represent the
“contract” between the software and the hardware. The effective allocation of the
resources happens according also to the (current) objective function in the system.
The objective function, as we said in Sect.
6.2.1
, defines which are the candidate re-
sources for the requesting application. A
QoS Estimator
component is employed for
the sole purpose of estimating the potential resource allocation, so that to compare
it with the application requirements. If an appropriate resource-to-task mapping is
found, then the allocation is given back to the application, that can now begin the de-
sired execution. The concept of “resource configuration” conveys in a single entity
any kind of resources: physical resources (e.g., assigned cores), logical resources
(e.g., clock cycles) and non-functional aspects (e.g., voltage/frequency selection for
power-constrained systems). For this reason, we may want to call such configuration
an
Operating Point
. In this perspective, the selection is performed by an
Operating
Point Selection
module. Such module implements the core of the RM. It is based on
two entities:
mechanisms
and
policies
. Mechanisms represent the observation and
control knobs that the underlying hardware (or the HAL software) provides for the
desired purpose, while policies define
how
resources to be allocated are selected.
From the description above, it is clear how an RTRM stays in the middle: it
takes software-related and application-specific constraints and retrieves information
from the underlying hardware platform. An overview of the RTRM in a system-
wide perspective is shown in Fig.
6.5
. Three different aspects are then taken into
Application aspects
Non-functional aspects
HP
LE
LP
SOFTWARE
APPLICATIONS
Constraints
assertion
Resources
allocation
R
TRM
Homogeneous
multi-core
HARDWARE PLATFORM
Single
core
HW
HW
HW
HW
Heterogeneous
many-core
Platform Aspects
Fig. 6.5
The RTRM takes into consideration application aspects, non-functional aspects and
platform aspects
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