Binoy Ravindran

An Optimal Real-Time Scheduling Algorithm for Multiprocessors

We present an optimal real-time scheduling algorithm for multiprocessors

Time-utility function-driven switched Ethernet: packet scheduling algorithm, implementation, and feasibility analysis

one that satisfies all task deadlines, when the total utilization demand does not exceed the utilization capacity of the processors. The algorithm called LLREF, is designed based on a novel abstraction for reasoning about task execution behavior on multiprocessors: the time and local execution time domain plane (or T-L plane). LLREF is based on the fluid scheduling model and the fairness notion, and uses the T-L plane to describe fluid schedules without using time quanta, unlike the optimal Pfair algorithm (which uses time quanta). We show that scheduling for multiprocessors can be viewed as repeatedly occurring T-L planes, and feasibly scheduling on a single T-L plane results in the optimal schedule. We analytically establish the optimality of LLREF. Further, we establish that the algorithm has bounded overhead, and this bound is independent of time quanta (unlike Pfair). Our simulation results validate our analysis on the algorithm overhead

On recent advances in time/utility function real-time scheduling and resource management

We present a MAC-layer, soft real-time packet scheduling algorithm called UPA. UPA considers a message model where message packets have end-to-end timeliness requirements that are specified using Jensens time-utility functions (TUFs). The algorithm seeks to maximize system-wide, aggregate packet utility. Since this scheduling problem is NP-hard, UPA heuristically computes schedules with a quadratic worst-case cost, faster than the previously best CMA algorithm. Our simulation studies show that UPA performs the same as or significantly better than CMA for a broad set of TUFs. Furthermore, we implement UPA and prototype a TUF-driven switched Ethernet system. The performance measurements of UPA from the implementation reveal its strong effectiveness. Finally, we derive timeliness feasibility conditions of TUF-driven switched Ethernet systems that use the UPA algorithm.

A utility accrual scheduling algorithm for real-time activities with mutual exclusion resource constraints

We argue that the key underpinning of the current state-of-the real-time practice - the priority artifact - and that of the current state-of-the real-time art - deadline-based timeliness optimality - are entirely inadequate for specifying timeliness objectives, for reasoning about timeliness behavior, and for performing resource management that can dependably satisfy timeliness objectives in many dynamic real-time systems. We argue that time/utility functions and the utility accrual scheduling paradigm provide a more generalized, adaptive, and flexible approach. Recent research in the utility accrual paradigm has significantly advanced the state-of-the-art of that paradigm. We survey these advances.

A formally verified application-level framework for real-time scheduling on POSIX real-time operating systems

This paper presents a uni-processor real-time scheduling algorithm called the generic utility scheduling algorithm (which we refer to simply as GUS). GUS solves a previously open real-time scheduling problem-scheduling application activities that have time constraints specified using arbitrarily shaped time/utility functions and have mutual exclusion resource constraints. A time/ utility function are a time constraint specification that describes an activitys utility to the system as a function of that activitys completion time. Given such time and resource constraints, we consider the scheduling objective of maximizing the total utility that is accrued by the completion of all activities. Since this problem is NP-hard, GUS heuristically computes schedules with a polynomial-time cost of O(n/sup 3/) at each scheduling event, where n is the number of activities in the ready queue. We evaluate the performance of GUS through simulation and by an actual implementation on a real-time POSIX operating system. Our simulation studies and implementation measurements reveal that GUS performs close to, if not better than, the existing algorithms for the cases that they apply. Furthermore, we analytically establish several properties of GUS.

Heterogenous Quorum-Based Wake-Up Scheduling in Wireless Sensor Networks

We present a framework, called meta scheduler, for implementing real-time scheduling algorithms. The meta scheduler is a portable middleware layer component designed for implementations over POSIX-compliant operating systems. It accommodates pluggable real-time scheduling algorithms while offering the flexibility of platform independence - the singular underlying OS requirement is the now nearly ubiquitous POSIX compliance. The versatility of pluggable schedulers positions the meta scheduler for deployment in an interoperable heterogeneous real-time environment. We present the design of the meta scheduler and outline its implementation. Furthermore, we present a mechanized correctness verification using the UPPAAL model checker. Prototype implementation of the meta scheduler over QNX Neutrino real-time operating system demonstrates high performance and a small footprint.

Probability-Based Prediction and Sleep Scheduling for Energy-Efficient Target Tracking in Sensor Networks

We present heterogenous quorum-based asynchronous wake-up scheduling schemes for wireless sensor networks. The schemes can ensure that two nodes that adopt different quorum systems as their wake-up schedules can hear each other at least once in bounded time intervals. We propose two such schemes: cyclic quorum system pair (cqs-pair) and grid quorum system pair (gqs-pair). The cqs-pair which contains two cyclic quorum systems provides an optimal solution, in terms of energy saving ratio, for asynchronous wake-up scheduling. To quickly assemble a cqs-pair, we present a fast construction scheme which is based on the multiplier theorem and the (N,k,M, l)-difference pair defined by us. Regarding the gqs-pair, we prove that any two grid quorum systems will automatically form a gqs-pair. We further analyze the performance of both designs, in terms of average discovery delay, quorum ratio, and energy saving ratio. We show that our designs achieve better trade-off between the average discovery delay and quorum ratio (and thus energy consumption) for different cycle lengths. We implemented the proposed designs in a wireless sensor network platform of Telosb motes. Our implementation-based measurements further validate the analytically-established performance trade-off of our designs.

Resource Management Middleware for Dynamic, DependableReal-Time Systems

A surveillance system, which tracks mobile targets, is one of the most important applications of wireless sensor networks. When nodes operate in a duty cycling mode, tracking performance can be improved if the target motion can be predicted and nodes along the trajectory can be proactively awakened. However, this will negatively influence the energy efficiency and constrain the benefits of duty cycling. In this paper, we present a Probability-based Prediction and Sleep Scheduling protocol (PPSS) to improve energy efficiency of proactive wake up. We start with designing a target prediction method based on both kinematics and probability. Based on the prediction results, PPSS then precisely selects the nodes to awaken and reduces their active time, so as to enhance energy efficiency with limited tracking performance loss. We evaluated the efficiency of PPSS with both simulation-based and implementation-based experiments. The experimental results show that compared to MCTA algorithm, PPSS improves energy efficiency by 25-45 percent (simulation based) and 16.9 percent (implementation based), only at the expense of an increase of 5-15 percent on the detection delay (simulation based) and 4.1 percent on the escape distance percentage (implementation based), respectively.

On Distributed Time-Dependent Shortest Paths over Duty-Cycled Wireless Sensor Networks

Thispaper presents resource management techniques that achieve thequality of service (QoS) requirements of dynamic real-time systemsusing open architectures and commercial off-the-shelf technologies(COTS). Dynamic real-time systems are subject to constant changessuch as a varying external environment, overload of internalsystems, component failure, and evolving operational requirements.Examples of such systems include the emerging generation of computer-based,command and control systems of the U.S. Navy. To enable the engineeringof such systems, we present adaptive resource management middlewaretechniques that achieve the QoS requirements of the system. Themiddleware performs QoS monitoring and failure detection, QoSdiagnosis, and reallocation of resources to adapt the systemto achieve acceptable levels of QoS. Experimental characterizationsof the middleware using a real-time benchmark illustrate itseffectiveness for adapting the system for achieving the desiredreal-time and survivability QoS during overload situations.

On multihop broadcast over adaptively duty-cycled wireless sensor networks

We revisit the shortest path problem in asynchronous duty-cycled wireless sensor networks, which exhibit time-dependent features. We model the time-varying link cost and distance from each node to the sink as periodic functions. We show that the time-cost function satisfies the FIFO property, which makes the time-dependent shortest path problem solvable in polynomial-time. Using the