Radu Cornea

Profile-Based Dynamic Voltage Scheduling Using Program Checkpoints

Dynamic voltage scaling (DVS) is a known effective mechanism for reducing CPU energy consumption without significant performance degradation. While a lot of work has been done on inter-task scheduling algorithms to implement DVS under operating system control, new research challenges exist in intra-task DVS techniques under software and compiler control. In this paper we introduce a novel intra-task DVS technique under compiler control using program checkpoints. Checkpoints are generated at compile time and indicate places in the code where the processor speed and voltage should be re-calculated. Checkpoints also carry user-defined time constraints. Our technique handles multiple intra-task performance deadlines and modulates power consumption according to a run-time power budget. We experimented with two heuristics for adjusting the clock frequency and voltage. For the particular benchmark studied, one heuristic yielded 63% more energy savings than the other. With the best of the heuristics we designed, our technique resulted in 82% energy savings over the execution of the program without employing DVS.

Integrated power management for video streaming to mobile handheld devices

Optimizing user experience for streaming video applications on handheld devices is a significant research challenge. In this paper, we propose an integrated power management approach that unifies low level architectural optimizations (CPU, memory, register), OS power-saving mechanisms (Dynamic Voltage Scaling) and adaptive middleware techniques (admission control, optimal transcoding, network traffic regulation). Specifically, we identify interaction parameters between the different levels and optimize them to significantly reduce power consumption. With knowledge of device configurations, dynamic device parameters and changing system conditions, the middleware layer selects an appropriate video quality and fine tunes the architecture for optimized delivery of video. Our performance results indicate that architectural optimizations that are cognizant of user level parameters(e.g. transcoded video quality) can provide energy gains as high as 57.5% for the CPU and memory. Middleware adaptations to changing network noise levels can save as much as 70% of energy consumed by the wireless network interface. Furthermore, we demonstrate how such an integrated framework, that supports tight coupling of inter-level parameters can enhance user experience on a handheld substantially.

A cross-layer approach for power-performance optimization in distributed mobile systems

The next generation of mobile systems with multimedia processing capabilities and wireless connectivity will be increasingly deployed in highly dynamic and distributed environments for multimedia playback and delivery (e.g. video streaming, multimedia conferencing). The challenge is to meet the heavy resource demands of multimedia applications under the stringent energy, computational, and bandwidth constraints of mobile systems, while constantly adapting to the global state changes of the distributed environment. In this paper, we present our initiatives under the FORGE framework to address the issue of delivering high quality multimedia content in mobile environments. In order to cope with the resource intensive nature of multimedia applications and dynamically changing global state (e.g. node mobility, network congestion), an end-to-end approach to QoS aware power optimization is required. We present a framework for coordinating energy optimizing strategies across various layers of system implementation and functionality and discuss techniques that can be employed to achieve energy gains for mobile multimedia systems.

FORGE: a framework for optimization of distributed embedded systems software

FORGE brings together a number of advances in architectural modeling, software architecture and distributed/real-time systems to build a platform that provides two fundamental capabilities for distributed, real time, and embedded (DRE) system development: (a) conceptualization and coding of the design knowledge through collaborative specifications that are inherently matched to distributed solutions; and (b) exploitation of the design knowledge across all development phases for the DRE systems. Our proof-of-concept FORGE prototype is built upon collaborative specifications captured by extensions to the message sequence charts (MSCs) that drive the customization of CompOSEIQ middleware services and generate node-architecture specific code through descriptions of the architecture and resources captured using ADL and RDL respectively.

Annotation Based Multimedia Streaming Over Wireless Networks

The relatively high power consumption of wireless network interfaces represents an important detriment in multimedia streaming for mobile devices. The IEEE 802.11 built-in power saving mode was designed for transfers of different nature and is not able to take advantage of the short idle intervals and continuous, periodic transmissions inherent in multimedia streaming. We propose an annotation based approach to wireless network power management that analyzes the variations in data transfer bandwidth during playback and uses the results to buffer data into larger burst transmissions with longer idle periods when the network card is transitioned into a lower power, sleep mode. Annotations allow for energy savings of up to 75% for the network interface, with practically no quality degradation or packet loss, only a small delay due to the buffer

Software Annotations for Power Optimization on Mobile Devices

Modern applications for mobile devices, such as multimedia video/audio, often exhibit a common behavior: they process streams of incoming data in a regular, predictable way. The runtime behavior of these applications can be accurately estimated most of the time by analyzing the data to be processed and annotating the stream with the information collected. We introduce a software annotation based approach to power optimization and demonstrate its application on a backlight adjustment technique for LCD displays during multimedia playback, for improved battery life and user experience. Results from analysis and simulation show that up to 65% of backlight power can be saved through our technique, with minimal or no visible quality degradation

Video Stream Annotations for Energy Trade-offs in Multimedia Applications

Recent applications for distributed mobile devices, including multimedia video/audio streaming, typically process streams of incoming data in a regular, predictable way. The behavior of these applications during runtime can be accurately predicted most of the time by analyzing the data to be processed and annotating the stream with the information collected. We introduce an annotation-based approach to power-quality trade-offs and demonstrate its application on CPU frequency scaling during video decoding, for an improved user experience on portable devices. Our experiments show that up to 50% of the power consumed by the CPU during video decoding can be saved with this approach

Architecture exploration of parameterizable EPIC SOC architectures

Design Space Exploration (DSE) of programmable systems-on-chip (SOC) incorporating parameterizable processor cores is difficult due to the complex and intrinsically nonstructured interactions between different architectural features of the processor (such as wide parallelism, and deep pipelines), the compiler and the application. Changing different processor features implies generating detailed operation conflict information - represented as Reservation Tables (RTs). If done manually, it can be a very tedious and error prone task, especially for deep pipelines, with complex resource sharing and large nonstructured instruction sets. In this paper we use RTGEN, an approach for automatic generation of RTs, to drive rapid architectural exploration of a large number of designs. We present exploration experiments on a large set of VLIW-like EPIC architectures, for varying port sharing, number of functional units, multicycling units, and with varied latency configurations. Our experiments uncovered several non-intuitive architecture design points, giving the system-level designer further flexibility in exploration of programmable SOC architectures.

Annotation Integration and Trade-off Analysis for Multimedia Applications

Multimedia applications for mobile devices, such as video/audio streaming, process streams of incoming data in a regular, predictable way. Content-aware optimizations through annotations allow us to highly improve the power savings at the various levels of abstraction: hardware/OS, network, application. However, in a typical system there is a continuous interaction between the components of the system at all levels, which requires a careful analysis of the combined effect of the aforementioned techniques. We investigate such an interaction and we describe metrics for estimating the effect various trade-off have on power and quality. By applying our metrics at the various abstraction levels we show how better energy savings can be achieved with lower quality degradations, through power-quality trade-offs and cross-layer interaction.

Architecture exploration of parameterizable EPIC SOS architectures (poster paper)

Design Space Exploration (DSE) of programmable systemson-chip (SOC) incorporating parameterizable processor cores is difficult due to the complex and intrinsically non-structured interactions between different architectural features of the processor (such as wide parallelism, and deep pipelines), the compiler and the application. Changing different processor features implies generating detailed operation conflict information – represented as Reservation Tables (RTs). If done manually, it can be a very tedious and error prone task, especially for deep pipelines, with complex resource sharing and large nonstructured instruction sets. In this paper we use RTGEN[2], an approach for automatic generation of RTs, to drive rapid architectural exploration of a large number of designs. We present exploration experiments on a large set of VLIW-like EPIC 1 architectures, for varying port sharing, number of functional units, multicycling units, and with varied latency configurations. Our experiments uncovered several non-intuitivearchitecture design points, giving the system-level designer further flexibility in exploration of programmable SOC architectures.