Dynamic Window-Constrained Scheduling for Real-Time Media Streaming

This paper describes an algorithm for scheduling packets in real-time multimedia data streams. Common to these classes of data streams are service constraints in terms of bandwidth and delay. However, it is typical for real-time multimedia streams to tolerate bounded delay variations and, in some cases, finite losses of packets. We have therefore developed a scheduling algorithm that assumes streams have window-constraints on groups of consecutive packet deadlines. A window-constraint defines the number of packet deadlines that can be missed in a window of deadlines for consecutive packets in a stream. Our algorithm, called Dynamic Window-Constrained Scheduling (DWCS), attempts to guarantee no more than x out of a window of y deadlines are missed for consecutive packets in real-time and multimedia streams. Using DWCS, the delay of service to real-time streams is bounded even when the scheduler is overloaded. Moreover, DWCS is capable of ensuring independent delay bounds on streams, while at the same time guaranteeing minimum bandwidth utilizations over tunable and finite windows of time. We show the conditions under which the total demand for link bandwidth by a set of real-time (i.e., window-constrained) streams can exceed 100% and still ensure all window-constraints are met. In fact, we show how it is possible to guarantee worst-case per-stream bandwidth and delay constraints while utilizing all available link capacity. Finally, we show how best-effort packets can be serviced with fast response time, in the presence of window-constrained traffic

Pinwheel Scheduling for Fault-tolerant Broadcast Disks in Real-time Database Systems

The design of programs for broadcast disks which incorporate real-time and fault-tolerance requirements is considered. A generalized model for real-time fault-tolerant broadcast disks is defined. It is shown that designing programs for broadcast disks specified in this model is closely related to the scheduling of pinwheel task systems. Some new results in pinwheel scheduling theory are derived, which facilitate the efficient generation of real-time fault-tolerant broadcast disk programs.National Science Foundation (CCR-9308344, CCR-9596282

MorphoSys: efficient colocation of QoS-constrained workloads in the cloud

In hosting environments such as IaaS clouds, desirable application performance is usually guaranteed through the use of Service Level Agreements (SLAs), which specify minimal fractions of resource capacities that must be allocated for unencumbered use for proper operation. Arbitrary colocation of applications with different SLAs on a single host may result in inefficient utilization of the host’s resources. In this paper, we propose that periodic resource allocation and consumption models -- often used to characterize real-time workloads -- be used for a more granular expression of SLAs. Our proposed SLA model has the salient feature that it exposes flexibilities that enable the infrastructure provider to safely transform SLAs from one form to another for the purpose of achieving more efficient colocation. Towards that goal, we present MORPHOSYS: a framework for a service that allows the manipulation of SLAs to enable efficient colocation of arbitrary workloads in a dynamic setting. We present results from extensive trace-driven simulations of colocated Video-on-Demand servers in a cloud setting. These results show that potentially-significant reduction in wasted resources (by as much as 60%) are possible using MORPHOSYS.National Science Foundation (0720604, 0735974, 0820138, 0952145, 1012798

Control and Communication-Schedule Co-design For Networked Control Systems

In a networked control system (NCS), the control loop is closed through a communication medium. This means that sensor measurements and/or control signals can be exchanged through a communication link. NCSs have many benefits, such as wiring reduction (elimination in the case of wireless communication), installation cost reduction, and simplification of upgrades and restructuring. However, network congestion, impairments of the wireless links (such as bandwidth limitations, packet losses, delays, and noises) may degrade system performance and even cause instability. These issues have motivated a great deal of research over the past 20 years and have given rise to a number of approaches to prevent congestion and compensate for delays and/or packet losses.An interesting class of NCSs that has not received enough attention is an NCS whose systems are uncertain and subject to state and inputs hard constraints.These hard constraints may stem from the system itself, its environment, or be proposed by the designer in order to guarantee safety or a certain performance.The contribution of this thesis is introducing a design framework that guarantees robust constraint satisfaction for a class of multi-agent NCSs with a shared communication medium that is subject to bandwidth limitation and prone to packet losses.The proposed framework is built upon reachability analysis to determine the communication demand for each system such that local constraints are satisfied and scheduling techniques to guarantee satisfaction of the communication demands. The thesis explores offline and online scheduling designs under various communication topologies, optimal control designs under state and output feedback, and scheduling and control co-design for NCSs with hard constraints

Vassal: Loadable Scheduler Support for Multi-Policy Scheduling

This paper presents Vassal, a system that enables applications to dynamically load and unload CPU scheduling policies into the operating system kernel, allowing multiple policies to be in effect simultaneously. With Vassal, applications can utilize scheduling algorithms tailored to their specific needs and general-purpose operating systems can support a wide variety of special-purpose scheduling policies without implementing each of them as a permanent feature of the operating system. We implemented Vassal in the Windows NT 4.0 kernel. Loaded schedulers coexist with the standard Windows NT scheduler, allowing most applications to continue being scheduled as before, even while specialized scheduling is employed for applications that request it. A loaded scheduler can dynamically choose to schedule threads in its class, or can delegate their scheduling to the native scheduler, exercising as much or as little control as needed. Thus, loaded schedulers can provide scheduling facilities and behaviors not otherwise availabl

Vassal: Loadable scheduler support for multi-policy scheduling

Abstract This paper presents Vassal, a system that enables applications to dynamically load and unload CPU scheduling policies into the operating system kernel, allowing multiple policies to be in effect simultaneously. With Vassal, applications can utilize scheduling algorithms tailored to their specific needs and general-purpose operating systems can support a wide variety of special-purpose scheduling policies without implementing each of them as a permanent feature of the operating system. We implemented Vassal in the Windows NT 4.0 kernel. Loaded schedulers coexist with the standard Windows NT scheduler, allowing most applications to continue being scheduled as before, even while specialized scheduling is employed for applications that request it. A loaded scheduler can dynamically choose to schedule threads in its class, or can delegate their scheduling to the native scheduler, exercising as much or as little control as needed. Thus, loaded schedulers can provide scheduling facilities and behaviors not otherwise available. Our initial prototype implementation of Vassal supports two concurrent scheduling policies: a single loaded scheduler and the native scheduler. The changes we made to Windows NT were minimal and they have essentially no impact on system behavior when loadable schedulers are not in use. Furthermore, loaded schedulers operate with essentially the same efficiency as the default scheduler. An added benefit of loadable schedulers is that they enable rapid prototyping of new scheduling algorithms by often removing the time-consuming reboot step from the traditional edit/compile/reboot/debug cycle. In addition to the Vassal infrastructure, we also describe a "proof of concept" loadable real-time scheduler and performance results

Attitude determination for small satellites using gps signal-to-noise ratio

Thesis (M.S.) University of Alaska Fairbanks, 2014An embedded system for GPS-based attitude determination (AD) using signal-to-noise (SNR) measurements was developed for CubeSat applications. The design serves as an evaluation testbed for conducting ground based experiments using various computational methods and antenna types to determine the optimum AD accuracy. Raw GPS data is also stored to non-volatile memory for downloading and post analysis. Two low-power microcontrollers are used for processing and to display information on a graphic screen for real-time performance evaluations. A new parallel inter-processor communication protocol was developed that is faster and uses less power than existing standard protocols. A shorted annular patch (SAP) antenna was fabricated for the initial ground-based AD experiments with the testbed. Static AD estimations with RMS errors in the range of 2.5° to 4.8° were achieved over a range of off-zenith attitudes