1. Manchester Computing S. M. Pickles, R. Haines, R. L. Pinning and A. R. Porter UK e-Science All Hands Meeting, 2004 2 nd September 2004 Practical Tools for Computational Steering Computational steering within the RealityGrid project

2. Supercomputing, Visualization and e-Science Group, Manchester Computing 2 Overview Computational steering in RealityGrid RealityGrid Steering API basics On-line Visualization Steering clients Some examples Summary

3. Manchester Computing Computational Steering in RealityGrid Motivation, approach and architecture…

4. Supercomputing, Visualization and e-Science Group, Manchester Computing 4 Motivation RealityGrid is a 3 year EPSRC e-Science pilot project Intended to bring Grid technology to bear in the field of condensed-matter physics, especially large-scale computer simulation We deal with existing scientific codes, typically parallel and written in F90, C or C++ Aim to provide generic tools to enable a physicist to make their own code steerable –They retain ownership of the code and the changes –They choose how much to implement – Avoid branching the source code into steerable and non-steerable versions –They are able to maintain the code in the future Performance is important – allow steering clients/visualizations to be attached and detached as required

5. Supercomputing, Visualization and e-Science Group, Manchester Computing 5 Approach Wish to retain flexibility while making it as easy as possible for a scientist to begin using computational steering Computational steering systems often tie the user to a specific visualization package or development/runtime environment We explicitly separate the steering functionality from any visualization capability –Can do one without the other –Reduces software dependencies –Lowers barrier to initial uptake of steering Adopt a component-based approach –Simulation, visualization & steering client are distinct components –Components can be run on different machines to suit their requirements –Allows our work to be taken-up in component-based frameworks Range of codes, platforms and languages  steering library in C

6. Supercomputing, Visualization and e-Science Group, Manchester Computing 6 Architecture – user’s view Simulation Visualization data transfer (binary) Client Steering library message transfer (XML)

7. Manchester Computing RealityGrid Steering API Basics

8. Supercomputing, Visualization and e-Science Group, Manchester Computing 8 RealityGrid Steering library Steering API implemented as a library in C –Can be called from F90, C and C++ –Library distribution includes F90 and C examples Library provides: –Pause/resume and stop –Set values of steerable parameters –Report values of monitored (read-only) parameters –Emit "samples" to remote systems for e.g. on-line visualization –Consume "samples" from remote systems for e.g. resetting boundary conditions –Checkpoint and restart –Automatic emit/consume with steerable frequency

9. Supercomputing, Visualization and e-Science Group, Manchester Computing 9 RealityGrid Steering API Basics - walkthrough Initialize lib & register supported commands (e.g. stop, pause) Register any steerable/monitored variables Register any “IOTypes” – used for emitting/consuming data sets –e.g. for sending data out for on-line visualization Register any “ChkTypes” – used for checkpoint management Call “Steering_control” from within the main loop of the code –Respond to any commands received from steering client –e.g. emit a data set, create and register a checkpoint, stop etc. Clean up when program finished

10. Supercomputing, Visualization and e-Science Group, Manchester Computing 10 RealityGrid Steering Library continued… No restriction on paradigm or harness for parallel codes Basic instrumentation is achieved with five calls to the library Reverse communication used –Library passes back instructions to the application (e.g. “take a checkpoint now”) Library contains both file- and SOAP/socket implementations –Steering messages read from/written to file or sent as SOAP messages to a Grid service interface to the application –Data sets read from/written to file or sent down a socket connection between applications –Code development can be performed free of Grid/networking complexity

11. Manchester Computing On-line Visualization Obtaining visual feedback from a simulation

12. Supercomputing, Visualization and e-Science Group, Manchester Computing 12 On-line Visualization Often, but not always, an important part of computational steering –Provides feedback to the scientist on the state of the simulation and the effect of any steering activity –A useful debugging aid RealityGrid steering library provides support for emitting and consuming data –May be used to construct the communication channel between simulation and visualization –Alternatively, any existing visualization functionality may be used The steering API is neutral to the implementation of the data IO –Steering library supports both file- and socket-based data transfer (chosen at compile time) –Socket connection established automatically if using Grid-service steering interface

13. Supercomputing, Visualization and e-Science Group, Manchester Computing 13 On-line Visualization cont’d… Typically use vtk with reader implemented using RealityGrid steering library Work underway on a data reader for AVS/Express In principle, visualization can be steerable but is normal to use visualization-specific GUI Component based architecture allows visualization to be run on any suitable machine –Images brought back to desktop using e.g. SGI VizServer, Chromium –Images broadcast to AccessGrid

14. Manchester Computing Steering clients Qt-based desktop steering client from MC.Net-based PDA steering client from Loughborough Web portal steering client from epcc

15. Supercomputing, Visualization and e-Science Group, Manchester Computing 15 Steering clients Desktop, Qt-based steering client –Real-time plotting of monitored parameters –Buffered data may be saved to file –Multiple simulations may be steered simultaneously –Can steer local & remote jobs –Control of IO and checkpointing –Requires Qt and Qwt to build –Has been ported to Windows XP

16. Supercomputing, Visualization and e-Science Group, Manchester Computing 16 Steering in Starbucks - PDA client Job screen Parameter screen Graph screen

17. Supercomputing, Visualization and e-Science Group, Manchester Computing 17 Steering over the web Developed by M Egbert of epcc Written in Java using GridSphere Minimal dependencies on client-side software

18. Manchester Computing Examples

19. Supercomputing, Visualization and e-Science Group, Manchester Computing 19 LBE3D - Lattice Boltzmann simulation of miscible fluids Parallel (MPI), F90 code Large number of steerable/monitored parameters (configured in input file) Control of output of ‘colour’ data field – allows progress of e.g. phase separation to be monitored via on-line visualization –visualization is bespoke vtk application using steering library to read data –Uses Tcl for GUI and event loop to allow automatic updates when new data available –Have integrated with Chromium for higher-resolution AG displays Pause facility (useful for demonstrations/deliberations)

20. Supercomputing, Visualization and e-Science Group, Manchester Computing 20 LBE3D functionality… Checkpoint, restart and rewind –LB3D registers all checkpoints it creates with the steering library –Checkpoint tree built up over time –Persistent record of work done (including all steering activity) –A running LBE3D can be requested to rewind Steering used to investigate phase space of oil/water/surfactant systems by adjusting strength of oil-water interaction –used with small models to inform what jobs to run with large models

21. Supercomputing, Visualization and e-Science Group, Manchester Computing 21

22. Manchester Computing NAMD

23. Supercomputing, Visualization and e-Science Group, Manchester Computing 23 Summary RealityGrid takes a component-based approach to steering and on-line visualization Application is instrumented by making calls to steering library Emphasis on enabling the scientist to do this themselves Steering library can also be used to send data to remote visualization Code and documentation available from http://www.sve.man.ac.uk/Research/AtoZ/RealityGrid/ Variety of steering clients available