Cradle PERF
Use Cradle-PERF for performance analysis of architecture and system design models. Operating on characteristics of behaviour, PERF can be used before functions are allocated, and before simulation is possible.
Performance assessment is complementary to simulation, or execution (such as timeline analysis). It does not rely on defined system behaviour, and can be used at the outset to define performance budgets for subsequent design levels (apportionment). Later, it can be used to aggregate from actual values.
Performance is expressed as user-defined characteristics, such as:
| • Bandwidth |
• Data rate |
| • Utilisation |
• Staleness |
| • Size |
• Weight |
| • Cost |
• Power |
These can be sub-divided (for example to study both best and worst case conditions) and are represented as user-defined formulae, created from a built-in library, user-defined table interpolations or look-ups, and user defined routines. Any number of characteristics can be defined, and associated with each diagram symbol.
With Cradle-REQ, system performance requirements are applied as constraints to these characteristics, and user-defined sets of diagrams are mathematically solved to quantify performance and confirm system viability; not violating the constraints. The resulting quantitative characteristics then form budgets for the next design level.
Operating scenarios, real data, constraints and environmental effects can be included and varied during analyses. Performance data and results are stored with the design in the database for subsequent analysis.
Results can be reported, exported as CSV for processing by data analysis tools or spread sheets, or can be graphed.
By being integrated into the models, performance data is cross referenced to performance requirements and original stakeholder needs and acceptance criteria.
PERF Applications
Performance assessment is used to set quantitative performance budgets for the next level of design. It therefore starts at the top of the system architecture, and cascades down into subsystems, equipments and so on.
Performance assessment begins by deciding which are the performance parameters (PPs) to be quantified. These PPs typically measure the how questions, such as How much data...? and How imprecise...? and How long...? PPs are chosen to answer each of these questions, so typical PPs will be such as STALENESS, THROUGHPUT, UTILISATION and DELAY. When PPs are defined, units should be specified and maximum and minimum values. Each PP is then described by a formula which defines its values in terms of the values of other PPs, typically either for the same diagram symbol, or the inputs to that symbol.
Performance requirements are applied to the architecture as a set of advisory or limiting constraints on the values of specific PPs.
The loading on the system from its environment is expressed as specific values applied to PPs in environmental input symbols. This loading is assembled from a 3-tier packaging of input conditions, environment conditions and environment loads. Input conditions are used to apply external PPs values at a specific point in the architecture.
A set of input conditions in an environment load will typically correspond to a single real world object, such as a sub-surface target. An environment load is then a set of these environment conditions, such as 4 sub-surface targets, and 5 surface targets, and represents a test case.
Analysing the performance means solving the model, which is a two stage pass through the diagrams in the model, solving the formulae. The results of these analyses are stored back into the PERF DATA frames of the definitions of the diagram symbols, from where they can be extracted as CSV files, into reports, or as graphs.
When investigating candidate system architectures, especially with reused, or shared components, a PERF analyses of each architecture identifies performance differences and helps to select the preferred architecture.
Results from each architecture analysis are quantitative values for each PP for each subsystem. These form the constraints for the PERF analysis of that subsystem, in which the performance budgets from the architecture analysis are decomposed into lower-level budgets for each equipment and component.
PERF analyses can be applied to collections of PADs, DFDs and FFBDs, depending on the diagram style used to model the system architecture.
|
