144 research outputs found
Rate Monotonic vs. EDF: Judgment Day
Since the first results published in 1973 by Liu and Layland on the Rate Monotonic (RM) and Earliest Deadline First (EDF) algorithms, a lot of progress has been made in the schedulability analysis of periodic task sets. Unfortunately, many misconceptions still exist about the properties of these two scheduling methods, which
usually tend to favor RMmore than EDF. Typical wrong statements often heard in technical conferences and even in research papers claim that RM is easier to analyze than EDF, it introduces less runtime overhead, it is more predictable in overload conditions, and causes less jitter in task execution.
Since the above statements are either wrong, or not precise, it is time to clarify these issues in a systematic fashion, because the use of EDF allows a better exploitation of the available resources and significantly improves system’s performance.
This paper comparesRMagainstEDFunder several aspects, using existing theoretical results, specific simulation experiments, or simple counterexamples to show that many common beliefs are either false or only restricted to specific situations
The Space of EDF Feasible Deadlines
It is well known that the performance of computer controlled systems is heavily affected by delays and jitter occurring in the control loops, which are mainly caused by the interference introduced by other concurrent activities. A common approach adopted to reduce delay and jitter in periodic task systems is to decrease relative deadlines as much as possible, but without jeopardising the schedulability of the task set. In this paper, we formally characterise the region of admissible deadlines so that the system designer can appropriately select the desired values to maximise a given performance index defined over the task set. Finally we also provide a sufficient region of feasible deadlines which is proved to be convex
The Multy Supply Function Abstraction for Multiprocessors
Multi-core platforms are becoming the dominant computing architecture for next generation embedded systems. Nevertheless, designing, programming, and analyzing such systems is not easy and a solid methodology is still missing. In this paper, we propose two powerful abstractions to model the computing power of a parallel machine, which provide a general interface for developing and analyzing real-time applications in isolation, independently of the physical platform. The proposed abstractions can be applied on top of different types of service mechanisms, such as periodic servers, static partitions, and P-fair time partitions. In addition, we developed the schedulability analysis of a set of real-time tasks on top of a parallel machine that is compliant with the proposed abstractions
Increasing the Confidence of Deep Neural Networks by Coverage Analysis
The great performance of machine learning algorithms and deep neural networks
in several perception and control tasks is pushing the industry to adopt such
technologies in safety-critical applications, as autonomous robots and
self-driving vehicles. At present, however, several issues need to be solved to
make deep learning methods more trustworthy, predictable, safe, and secure
against adversarial attacks. Although several methods have been proposed to
improve the trustworthiness of deep neural networks, most of them are tailored
for specific classes of adversarial examples, hence failing to detect other
corner cases or unsafe inputs that heavily deviate from the training samples.
This paper presents a lightweight monitoring architecture based on coverage
paradigms to enhance the model robustness against different unsafe inputs. In
particular, four coverage analysis methods are proposed and tested in the
architecture for evaluating multiple detection logics. Experimental results
show that the proposed approach is effective in detecting both powerful
adversarial examples and out-of-distribution inputs, introducing limited
extra-execution time and memory requirements
Limited Preemptive Scheduling for Real-Time Systems: a Survey
The question whether preemptive algorithms are better than nonpreemptive ones for scheduling a set of real-time tasks has been debated for a long time in the research community. In fact, especially under fixed priority systems, each approach has advantages and disadvantages, and no one dominates the other when both predictability and efficiency have to be taken into account in the system design. Recently, limited preemption models have been proposed as a viable alternative between the two extreme cases of fully preemptive and nonpreemptive scheduling. This paper presents a survey of the existing approaches for reducing preemptions and compares them under different metrics, providing both qualitative and quantitative performance evaluations
FTT-Ethernet: A Flexible Real-Time Communication Protocol that Supports Dynamic QoS Management on Ethernet-based Systems
Ethernet was not originally developed to meet the
requirements of real-time industrial automation systems and
it was commonly considered unsuited for applications at the
field level. Hence, several techniques were developed to make
this protocol exhibit real-time behavior, some of them requiring
specialized hardware, others providing soft-real-time guarantees
only, or others achieving hard real-time guarantees with
different levels of bandwidth efficiency. More recently, there has
been an effort to support quality-of-service (QoS) negotiation
and enforcement but there is not yet an Ethernet-based data
link protocol capable of providing dynamic QoS management
to further exploit the variable requirements of dynamic applications.
This paper presents the FTT-Ethernet protocol, which
efficiently supports hard-real-time operation in a flexible way,
seamlessly over shared or switched Ethernet. The FTT-Ethernet
protocol employs an efficient master/multislave transmission
control technique and combines online scheduling with online
admission control, to guarantee continued real-time operation
under dynamic communication requirements, together with data
structures and mechanisms that are tailored to support dynamic
QoS management. The paper includes a sample application,
aiming at the management of video streams, which highlights
the protocol’s ability to support dynamic QoS management with
real-time guarantees
Towards a muon collider
A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work
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