DDT is a parallel debugger from Allinea. It has a graphical user interface and can be used for debugging Fortran, C, and C++ programs that have been parallelized with MPI and OpenMP, as well as UPC programs. Additional information can be found at http://www.allinea.com/products/ddt.
MAP is a low-overhead profiler from Allinea for both scalar and MPI programs.
Both tools share a common environment.
In most cases it is much faster and easier to find an error in the code or the ways to optimize the performance using a debugger and a profiler than through the use of numerous print statements.
The Allinea DDT and MAP user guide can be downloaded from http://content.allinea.com/downloads/userguide.pdf.
The Allinea Sogtware Blog has various articles on how to best utilize the Allinea tools, such as how to fix dangling pointers or debug mixed Python and Fortran codes.
First of all make sure that your environment is set up so you can use DDT and MAP. Issue
which ddtYou should get
/shared/allinea/forge/bin/ddtSame applies to map.
Next check whether your desktop computer accepts X connections. Issue
xterm &If your desktop machine accepts X connections, then this command will open a window.
If no window was open, try to login to Condo cluster issuing the following commands:
ssh -X condo.its.iastate.eduand once logged to 'condo', issue "xterm &".
You can also try to set environment variable DISPLAY to tell condo which machine to display the DDT window on:
setenv DISPLAY desktop_machine_name:0.0To find out the desktop_machine_name, issue on condo:
If nothing of the above works, then you will need to find another desktop computer to be able to use DDT.
Alternatively you can install a remote client on your desktop which you can download from http://www.allinea.com/products/downloads. After installing the remote client, start the program and set up the Remote Launch by entering the following in the Host Name field:
<user>@condo.its.iastate.eduwhere <user> is your user name on condo. In the Remote Installation Directory field enter
/shared/allinea/forgeSee details in the Allinea DDT and MAP User Guide.
To provide debugger with the information about the program, the program should be compiled with a debug flag. For the compilers installed on Condo cluster, this is "-g". To start DDT type either of the following:
ddt ddt program_name [arguments]The Allinea DDT and MAP User Guide explains in more details how to debug and profile programs. You can also use the following example to get acquainted with DDT.
cp /home/SAMPLES/mpihello.c ./
mpiicc -g mpihello.c
ddt &First a small windows saying "Allinea FORGE" will open, then it will be replaced by a larger window.
Click on RUN to run and debug a program.
In the application field enter the full path of the executable that you would like to debug. If you issued the cp command above from your home directory, enter "/home/<user>/a.out", where <user> is your user name on condo. You can also search for executable by clicking on the yellow folder button on the right of the application field.
Select checkboxes by "MPI" and "Submit to Queue" options.
Click on the "Configure..." button in the "Submit to Queue" option.
In the "Submission template file" field enter "/shared/allinea/forge/templates/condo.qtf". After entering this, four other fields will be populated.
Click on "OK" button.
In the MPI section select 4 processes, 2 nodes and 2 processes per node. You can link number of processes with number of nodes by clicking on the chain sign on the right. In this case DDT will make sure that all 3 parameters are consistent, so change it one parameter will automatically cause the change in another parameter.
In the mpirun arguments field enter "-ppn 2", so that 2 MPI processes will be placed on every node.
Click on "Submit" button at the bottom.
DDT will submit your job into queue. When job will start running, DDT will attach to the processes. In the central part of the window you will see the code.
Right-click on line 18 (on the line number) and select "Add breakpoint for All". Do the same at line 21.
Click on the green triangle in the upper left corner of the window. A small window should appear telling that processes 0-3 stopped at breakpoint in line 18. Click on "Pause".
Explore the information provided in the lower part of the window (click on different tabs) and the values of variables displayed on the right. Select ping squares with numbers 0 through 3 to see information for various processes. Notice that MyId will have different values for different processes (select the Locals tab to see local variables), name will have some garbage in it.
Once again click on the green triangle in the upper left corner of the window. The processes will be stopped at the next breakpoint, and a small notification window will appear. Select "Pause" and see what changed. In the Input/Output window you should now see Hello messages from all 4 processes, and in the variable window name should now have the correct value.
To finish the execution, click on the green triangle, and when prompted about restarting session, select "No".
You can start new session by selecting appropriate menu option in the File menu.
The following is a list of the important functions allowed by DDT:
Stepping through the program one statement at a time and displaying all variable values.
Running the program to a selected statement where a breakpoint has been set and then displaying variable values.
Stepping into and out from functions/subprograms.
Running a program and having the program stop execution where a problem occurs. Then one knows where the program stopped execution and values of variables at that point.
Stepping can be done with all MPI processes stepping together or selected MPI processes stepping independently.
The following summarizes the most useful items from the toolbars at the top of the DDT window:
File: restart and exit sessions, configure DDT
Edit/Go to Line: allows one to easily go to any line of the program displayed in the middle window and to search for strings.
Window: allows one turn on and off viewing of various items.
Help: allows one to view and print the DDT User Guide and displays a FAQ.
Control/Focus on current: Allows one to select group, process or thread for stepping through the program.
Play: starts program execution from where it was stopped and runs to the next breakpoint or until the program stops.
Pause: pauses program execution on all MPI processes.
Step Into: execution proceeds into the function/subroutine if stopped at a function or subroutine; otherwise, execution continues to the next statement.
Step Over: execution continues to the next statement and not into a function/subroutine.
Step Out: allows one to step out from a function/subroutine.
Values of local variables are displayed in the right center window for the MPI process selected for the place where execution has stopped. Multi-dimensional array values can be viewed by selecting Multi-Dimensional Array Viewer listed under View.