VTT's ABSOLUT approach reduces costs and risks in system design
ABSOLUT is a system-level performance simulation approach intended for early evaluation of embedded computer systems, and for exploring the design space. It is also a set of tools to assist the designer with application and platform modelling, allocation and configuration, simulation and result visualisation.
ABSOLUT has been the subject of several research projects for almost ten years, in cooperation with Nokia, Thales, Intracom, Tampere University of Technology and others. It has been applied to several case studies, ranging from contemporary mobile phone platforms to future high-performance systems consisting of hundreds of components.
The ABSOLUT performance evaluation approach provides low modelling effort through proper abstractions in order to solve the complexity problem, while maintaining enough accuracy for reliable evaluation results. Early evaluation is achieved since the modelling or simulation of complete systems is not dependent on mature hardware or software.
Applications are modelled as layered workload models ultimately consisting of abstract, instruction-like workload primitives. Several techniques have been developed for creating workload models from information sources such as application specifications or execution traces. Compiler-based tools exist to create workload models automatically from application source code.
Abstracting application functionality also reduces the complexity of execution platform models. There is no need for detailed modelling of the data paths of processing elements, and data transfers and storage are only simulated from the performance point of view. With the help of a supporting tool, a platform model can be constructed rapidly from components in a model library.
A virtual system model is constructed by allocating workload models on platform components. The model is simulated using the IEEE standard SystemC kernel and models based on the TLM standard. Performance, power and energy consumption data is obtained from simulations by instrumenting the models with custom performance probes. The designer can freely insert the probes into the models to extract, for example, resource utilisation, execution latencies or interconnection traffic.
ABSOLUT has been applied to a number of case studies, including mobile phone usage, MP3 playback, MPEG4 encoding and decoding, 3D gaming, virtual network computing and parallel software-defined radio applications. The platforms used in the studies represent both embedded systems and personal computers, and at the same time both currently existing platforms and future designs. Some of the results obtained from simulations have been compared to measurements from real platforms, revealing an average difference of 12% in the results. This exceeds the accuracy requirements expected from simulation approaches based on virtual systems, intended for early evaluation.
Tools and customisation
The ABSOLUT tool set consists of the following:
- A workload model generator based on the open source GCC compiler with shared library support.
- A component library for platform modelling, which includes processors (ARM, Intel), interconnects and memories.
- A platform model generation and configuration system.
- A transaction-level simulator utilising the OSCI SystemC 2.3 kernel.
- A visualisation tool for displaying resource utilisation and power consumption graphically.
VTT is able to rapidly customise ABSOLUT into production use. Customisations can include adaptation of workload modelling tools and techniques, modification of result formats, scripting, etc.