Escali 4.4 Built-in-tools for debugging, Assistance for external profiling, Legal options are

Section: 3.7 Debugging and profiling

3.7.2 Built-in-tools for debugging

Built-in tools for debugging in Scali MPI Connect covers discovery of the MPI calls used through tracing and timing, and an attachment point to processes that fault with segmentation violation. The tracing and timing is covered in Chapter 4.

3.7.2.1 Using built-in segment protect violation handler

When running applications that terminate with a SIGSEGV-signal it is often useful to be able to freeze the situation instead of exiting, the default behavior. The built-in SIGSEGV-handler can be made to do this by defining the environment-variable

SCAMPI_INSTALL_SIGSEGV_HANDLER.

Legal options are:

6.The handler dumps all registers and starts looping. Attaching with a debugger will then make it possible to examine the situation which resulted in the segment protect violation.

7.The handler dumps all registers but all processes will exit afterwards.

All other values will disable the installation of the handler.

To attach to process <pid> on a machine with the GNU debugger (gdb) do;

user% gdb /proc/<pid>/exe <pid>

In general, this will allow gdb to inspect the stack trace and identify the functions active when the sigsegv occurred, and disssasemble the functions. If the application is compiled with debug info (-g) and the source code is available, then source level debugging can be carried out.

3.7.3 Assistance for external profiling

Profiling parallel applications is complicated by having multiple processes at the same time. But Scali MPI Connect comes to assistance; through the SCAMPI_PROFILE_APPLICATION environment variable together with the -separate_outputoption (SCAMPI_SEPARATE_OUTPUT) the output from the application runs is directed at one file per process for easier use.

The environment variables SCAMPI_PROFILE_APPLICATION_START and

SCAMPI_PROFILE_APPLICATION_END are also available for steering the range of memory addresses applicable to profiling.

3.7.4 Debugging with Etnus Totalview

SMC applications can be debugged using the Etnus Totalview, see http://www.etnus.com for more information about this product.

To start the Etnus Totalview debugger with a Scali MPI application, use the tvmpimon wrapper script. This wrapper script accepts the regular options that mpimon accepts, and sets up the environment for Totalview. The totalview binary must be in the search path when launching tvmpimon. If the mpirun script is the preferred way of starting jobs, it accepts the “standard” -tv option, however the same rules applies with regards to the search path.

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