Debugging OpenMPI jobs

 

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As someone else said, TotalView is the standard for this. But it will cost you an arm and a leg.

The OpenMPI site has a great FAQ on MPI debugging. Item #6 in the FAQ describes how to attach GDB to MPI processes. Read the whole thing, there are some great tips.


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Debugging

Starting jobs with a debugger

Up: Debugging Next: Starting the debugger when an error occurs Previous: Error handlers

The -dbg=<name of debugger> option to mpirun causes processes to be run under the control of the chosen debugger. For example, enter

mpirun -dbg=gdb or mpirun -dbg=gdb a.out
invokes the mpirun_dbg.gdb script located in the mpich/bin directory. This script captures the correct arguments, invokes the gdb debugger, and starts the first process under gdb where possible. There are five debugger scripts; ddd, gdb, xxgdb, ddd, and totalview. These may need to be edited depending on your system. There is another debugger script for dbx, but this one will always need to be edited as the debugger commands for dbx varies between versions. You can also use this option to call another debugger; for example, -dbg=mydebug. All you need to do is write a script file, mpirun_dbg.mydebug, which follows the format of the included debugger scripts, and place it in the mpich/bin directory. More information on using the Totalview debugger with mpich can be found in Section Debugging MPI programs with TotalView .

Starting the debugger when an error occurs


Up: Debugging Next: Attaching a debugger to a running program Previous: Starting jobs with a debugger

It is often convenient to have a debugger start when a program detects an error. If mpich was configured with the option --enable-mpedbg, then adding the command-line option -mpedbg to the program will cause mpich to attempt to start a debugger (usually dbx or gdb) when an error that generates a signal (such as SIGSEGV) occurs. For example,

mpirun -np 4 a.out -mpedbg
If you are not sure if your mpich provides this service, you can use -mpiversion to see if mpich was built with the --enable-mpedbg option. This feature may not be available with all devices.

Debugging SGI MPI Applications

TotalView can acquire processes started by SGI MPI, which is part of the Message Passing Toolkit (MPT) 1.3 and 1.4 packages.

Message queue display is supported by release 1.3 and 1.4 of the Message Passing Toolkit. See Displaying the Message Queue Graph for message queue display.

SGI MPI programs are normally started by using the mpirun command. You would use a similar command to start an MPI program under TotalView's control:

{ totalview | totalviewcli } mpirun -a mpirun-command-line

This invokes TotalView and tells it to show you the machine code for mpirun. Since you're not usually interested in debugging this code, use the Process > Go command to let the program run.

CLI Equivalent: dfocus p dgo

The SGI MPI mpirun command runs and starts all MPI processes. After TotalView acquires them, it asks if you want to stop them at startup. If you answer Yes, TotalView halts them before they enter the main program. You can then create breakpoints.

If you set a verbosity level that allows informational messages, TotalView also prints a message showing the name of the array and the value of the array services handle (ash) to which it is attaching.

Attaching to an SGI MPI Job

To attach to a running SGI MPI job, attach to the SGI MPI mpirun process that started the job. The procedure for attaching to an mpirun process is the same as the procedure for attaching to any other process. For details, see Attaching to Processes.

After you attach to the mpirun process, TotalView asks if you also wish to attach to slave MPICH processes. If you do, press Return or choose Yes. If you do not, select No.

If you choose Yes, TotalView starts the server processes and acquires all MPICH processes.

As an alternative, you can use the Group > Attach Subsets command to predefine what TotalView should do. For more information, see Attaching to Processes.

Debugging OpenMP code (Darryl Gove's blog)

Debugging OpenMP code

By Darryl Gove on Oct 10, 2007

The compiler flag -xopenmp enables the recognition of OpenMP directives. As a side -effect it also raises the optimisation level to -xO3. If you're trying to debug the code, then you'll not want the optimisation level raised then you can use the option -xopenmp=noopt which enables the recognition of OpenMP directives but does not increase the optimisation level.

It's also worth compiling with the flags -xvpara and -xloopinfo which report parallelisation information.

Debugging OpenMP Applications TotalView User Guide (v6.3)

Debugging with DDT on the clusters - Research Computing

Chapter 13 Debugging OpenMP Programs (Sun Studio 12 Debugging a Program With dbx)

  1. [PDF]

    Debugging and Optimizing MPI and OpenMP™ …

Debugging MPI By Dave Hadka | Water Programming: A ...

Debugging - High Performance Computing (HPC) - University Wiki



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