Martin Pohlack

Rotational-position-aware real-time disk scheduling using a dynamic active subset (DAS)

Scheduling disk requests with service guarantees has to bring the demand to meet guarantees in line with the need to optimize disk utilization. This paper presents the design, implementation, and experimental evaluation of a disk-scheduling framework which optimizes the disk utilization under the constraints of both hard and statistical service guarantees. The framework is based on two principles: 1) upon each scheduling decision, the calculation of a subset of the outstanding disk requests such that all service guarantees can be enforced under worst-case assumptions; and 2) the scheduling of this subset based on the rotational position of requests in order to improve the disk utilization. Results are presented through an implementation of the scheduling framework in DROPS, the Dresden real-time operating system.

Principles for the Prediction of Video Decoding Times Applied to MPEG-1/2 and MPEG-4 Part 2 Video

In this paper, we present a method to predict per-frame decoding times of modern video decoder algorithms. By examining especially the MPEG-1, MPEG-2, and MPEG-4 pt. 2 algorithms, we developed a generic model for these decoders, which also applies to a wide range of other decoders. From this model, we derived a method to predict decoding times with an up-to-now unmatched accuracy while keeping the overhead low. We show the effectiveness of this method with an example implementation and compare the resulting predictions with the actual decoding times using video material from commercial DVDs

Enforceable component-based realtime contracts

We present enforceable component-based realtime contracts, the first extension of component-based software engineering technology that comprehensively supports adaptive realtime systems from specification all the way to the running system.To provide this support, we have extended component-based interface definition languages (IDLs) and component representations in repositories to express realtime requirements for components. The final software, which is assembled from the components, is then executed on a realtime operating system (RTOS) with the help of a component runtime system. RTOS resource managers and the IDL-extensions are based on the same mathematical foundation. Thus, the component runtime system can use information expressed in a component-oriented manner in the extended IDL to derive parameters for the task-based admission and scheduling in the RTOS. Once basic realtime properties can thus be guaranteed, runtime support can be extended to more elaborate schemes that also support adaptive applications (container-managed quality assurance).We claim that this study convincingly demonstrates how component-based software engineering can be extended to build systems with non-functional requirements.

The COMQUAD component container architecture

Component-based applications require runtime support to be able to guarantee non-functional properties. This paper proposes an architecture for a real-time-capable, component-based runtime environment, which allows to separate non-functional and functional concerns in component-based software development. The architecture is presented with particular focus on the real-time-non-real-time split of the runtime environment and the communication issues of respective component types and container parts.

Video quality and system resources: Scheduling two opponents

In this article we present three key ideas which together form a flexible framework for maximizing user-perceived quality under given resources with modern video codecs (H.264). First, we present a method to predict resource usage for video decoding online. For this, we develop and discuss a video decoder model using key metadata from the video stream. Second, we explain a light-weight method for providing replacement content for a given region of a frame. We use this method for online adaptation. Third, we select a metric modeled after human image perception which we extend to quantify the consequences of available online adaptation decisions. Together, these three parts allow us, to the best of our knowledge for the first time, to maximize user-perceived quality in video playback under given resource constraints.