Design and Optimization of Adaptive Multimedia Systems –Challenges, Approaches and Opportunities
The tutorial will have five parts.
PART 1 – Introduction
In this section we will cover motivation, objectives and outline of the rest of the tutorial.
This will have the following FOUR sub-sections
(a) What is the problem and why should multimedia system designers/researchers be interested in it?
(b) What are the recent developments in technology that enable a new way of thinking?
(c) What is missing?
A systematic methodology that takes advantage of the recent developments in algorithms and hardware platforms to design and optimize multimedia algorithms while satisfying the constraints imposed by emerging applications in universal multimedia access. So, that is what we will try to address in this tutorial and thereby unravel new opportunities for hardware architects, system designers and application/algorithm designers
(d) OUTLINE OF THE REST OF THE PRESENTATION:
We will describe approaches that some of us are developing that addresses the concerns listed above. In Part II, we will describe a framework to extend traditional rate-distortion theory to incorporate a notion of complexity in a generic way. This provides a framework for formulating the construction of multifidelity or complexity scalable algorithms as a classic (non-linear) optimization problem and use standard methods like dynamic programming, Lagrangian methods etc. In Part III, we will describe configurable hardware platforms with examples from our recent work on tile-based architectures for embedded processors, granularity studies, aggressive voltage scaling (or voltage overscaling), multi-voltage caches and opportunities for reconfigurable logic in implementing future multimedia apps. In Part IV, we will describe a systematic technique for workload shaping based on abstracting complexity. This will help us deal with the problems imposed by the heterogeneity of embedded devices. In Part V, we will focus on a complete case study – i.e. energy-aware system design for wireless multimedia, where an integrated approach to energy management is proposed that addresses cross-layer optimization issues.
PART II - Complexity Modeling
· Complexity Basis Functions
· Rate-Distortion-Complexity Models
· Complexity Scalable Algorithm – motion-compensation example perhaps
· Formulation of the optimization problem to select an operating point given resource constraints such as energy or processing power. If space is an issue, we can skip this or merge it with Part IV.
PART III - Programmable Hardware Architectures
We will cover some of the new developments in the horizon beyond DVS (dynamic voltage scaling) and Configurable Caches. To satisfy the increased complexity in terms of processing power and multiple processes tile-based chip-level multiprocessors will be required. We are already seeing this in network processors and future multimedia processors will follow. The question then is - how are they architected and what are their tunable knobs? In that context, what is the right granularity of a tile becomes very relevant? Should I use 2 simple Blackfin or C55x DSPs or should I go with a 4-way VLIW? Next, we will describe an aggressive approach to voltage scaling, namely voltage overscaling i.e. deliberately compromising reliability in the hope of saving power. I will draw examples circuit-level speculation, algorithmic noise tolerance and our recent work on power versus reliability trade-offs in data caches and multi-voltage data caches. Finally, we will show some new opportunities for dynamically reconfigurable logic in the complexity scalable implementation of wavelet based video decoders. We will draw this material from the following recent papers of ours
· Synchroscalar design issues from our ISCA 2004 paper
· Impact of granularity on power consumption of a tile-based processors
· Voltage Overscaling - trading power for reliability
· Opportunities for Dynamically Reconfigurable Logic
PART IV – Workload Modeling and Reshaping
The problem that is addressed here is - Given a programmable hardware platform with a set of knobs, that represent different resource utilization versus performance configurations or hardware operating points, how can the applications choose the optimal operating point and track the operating point under time varying operating conditions and data inputs. The emphasis will be on formalizing the methodology. There are four challenges that need to be addressed: (a) Workload modeling (b) Efficient algorithms for reconfiguration and (c) Workload reshaping just like traffic reshaping to meet the resource constraints at the end user and (d) Dealing with heterogeneous architectures and platforms.
In terms of workload modeling, there can be on-line models like those developed by the GRACE project @ UIUC or offline models like what we @ UC Davis have been doing. In terms of algorithms for reconfiguration we will discuss reactive and proactive techniques and their trade-offs. Heterogeneity will be addressed by our notion of generic complexity metrics and translating them into real complexity metrics at run-time and finally we will talk about the need for hardware abstraction layers in future hardware platforms for run-time resource measurement and reconfiguration.
I will draw the material for this section from our recent ICASSP and ICME 2005 papers and the topics will include:
· Workload Modeling – Generic Complexity Metrics
· On-line versus off-line models
· GCM to RCM translation and validation and using it for DVS
· Workload Reshaping using models for slack and slack borrowing/accumulation with and without comprising distortion
· We will integrate complexity modeling and complexity scalable algorithms as part of the workload reshaping problem with reduction in quality/distortion
· Other sources and pointers are appreciated
PART 5 - SYSTEM LEVEL DESIGN –
The concepts and techniques that have been discussed so far are actually being implemented and tested at some universities such as UC Irvine. Preliminary results are quite promising.
So, we will wrap up with a complete case study of energy aware system design methodology being experimented at UC Irvine as part of the FORGE and DYNAMO projects. It illustrates a specific example of integrated system level design for wireless multimedia. The key features of this are cross-layer optimization, i.e. how the middleware, operating system and network and hardware platform are jointly optimized for a given quality of service. This will illustrate the potential benefits of such an integrated approach. The role of intelligent proxies is considered. Tools and technique for rapid prototyping will be considered.