The tests programs

During the 1st semester, in the Message Parsing Programming lectures, EPPC staff taught us how to use the basic features of MPI, and how to avoid some mistakes. For this project some example will be reused to insure that both the profiler and display work correctly

The Message in a Ring

The message in a ring is a simple MPI program where each process sends data to the next one and receive therefore from the previous one. This program was developed to investigate the difference between the several send and receive possibilities proposed by the MPI standard:

• Asynchronous send ; receive ; wait for the send
• Asyncrhonous receive ; send ; wait for receive
• Use of the special send and receive function

This code can be used as an example of real time communication, and checking on waiting for communications.

Calculating PI

The calculating PI was an exercise where each processor was computing a part of PI and then a reduction is done to add the results together. The goal was to illustrate the possible rounding errors when the sum wasn't done in the same order. In order to avoid it, an array was made on the master processor to store each result and do the sum in the end.

This code can be used to show a very simple data registering (float).

The traffic model

The traffic model simulation was a simple domain decomposition model, where a process can have several cells of road. Each cell can be either occupied or empty. A car moves to an empty cell forward to it. Therefore some communication has to be made to send cars across the neighbour processors: check if the next cell is empty (a very simple 1D hallow swapping).

The casestudy and coursework

The idea was to introduce a very simple reverse edge detection algorithm. The solution is quite computing intensive as a smooth operation has to be made several time in order to obtain the original picture. Therefore a simple domain decomposition was done on 1 of the dimension to share the work among processors.

This code involves typical hallo swapping and the use of MPI datatypes.

The coursework introduces a 2D domain decomposition. Making it more complex to share data with the neighbours processes.

Meeting 3 and 4 [21/02 and 14/03]

During the month of March the deadline for the Project Preparation report and presentation. The goal of this module was to justify the research done and to prove the feasibility of the project.

During the 3rd meeting the MPI socket organisation was presented to David, showing a new orientation of the communication. Mainly the discussion was about the report, and what to write in it.

But also a set of tests, from the earlier MPI course, was discussed, including 3 simple codes and 1 more complex one:

• calculating PI
• A message in a ring
• The traffic model

With the willing to be able to use the MPI casestudy and its evolution: the coursework. This last was about an image computing. All tests will be discuss later in this blog.

The main features for the software are the communication information (general statistics to find missing calls to MPI_Wait for example), the data display to show what data are sent and where they are stored to. Finally the last feature is a synchronised view of the communication, equivalent to a step by step action in a debugger, but at a MPI call level rather than a C or assembly one.

Few innovations were made for the 4th meeting. The report was due few days after. Nonetheless some goals were discuss. The project will provide a framework composed of a library (the profiler part) and an executable (the interface). The goal is to provide a real time global view of the program and it aims modest MPI programs with few processes. As it is only an information tool no performance is needed, but effort will be made to insure at least memory management.