NAME¶
MPIL_Trace_off - LAM/MPI-specific function to disable run-time tracing
SYNOPSIS¶
#include <mpi.h>
int MPIL_Trace_off(void)
NOTES¶
These functions give the application the flexibility to generate traces only
during certain interesting phases of the application's execution. This
technique can considerably reduce the size of the trace files and burden of
displaying them.
Both functions are collective over the
MPI_COMM_WORLD communicator. In
typical usage, the
-toff option of
mpirun (1) would be used to
enable tracing, but start with the runtime switch in the off position. At the
beginning of an interesting phase of program execution,
MPIL_Trace_on
would be called.
MPIL_Trace_off would be called after the interesting
phase. Tracing can be turned on and off many times. Each period of tracing
eventually forms a trace segment in the trace file extracted by
lamtrace (1). If the on/off functions are never used and tracing is
enabled with the
-ton option of
mpirun (1), a single trace
segment is produced.
The on/off functions have no effect if tracing is not enabled by
mpirun
(1) with either the
-ton or
-toff switches. Thus, an application
can be littered with these functions but run without trace collection and very
little additional overhead due to the no-operation function calls.
This is a LAM/MPI-specific function and is intended mainly for debugging. If
this function is used, it should be used in conjunction with the
LAM_MPI C preprocessor macro
#if LAM_MPI
MPIL_Trace_off();
#endif
LIMITATIONS¶
After the volume of generated traces exceeds a preset limit, the oldest traces
are discarded in favour of new traces. Avoiding discarded traces is further
incentive to use
MPIL_Trace_on and
MPIL_Trace_off .
NOTES FOR FORTRAN¶
All MPI routines in Fortran (except for
MPI_WTIME and
MPI_WTICK )
have an additional argument
ierr at the end of the argument list.
ierr is an integer and has the same meaning as the return value of the
routine in C. In Fortran, MPI routines are subroutines, and are invoked with
the
call statement.
All MPI objects (e.g.,
MPI_Datatype ,
MPI_Comm ) are of type
INTEGER in Fortran.
ERRORS¶
If an error occurs in an MPI function, the current MPI error handler is called
to handle it. By default, this error handler aborts the MPI job. The error
handler may be changed with
MPI_Errhandler_set ; the predefined error
handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned (in C and Fortran; this error handler is less useful in with the C++
MPI bindings. The predefined error handler
MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI
does
not guarantee that an MPI program can continue past an error.
All MPI routines (except
MPI_Wtime and
MPI_Wtick ) return an error
value; C routines as the value of the function and Fortran routines in the
last argument. The C++ bindings for MPI do not return error values; instead,
error values are communicated by throwing exceptions of type
MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not
MPI::SUCCESS .
Note that if the
MPI::ERRORS_RETURN handler is set in C++, while MPI
functions will return upon an error, there will be no way to recover what the
actual error value was.
- MPI_SUCCESS
- - No error; MPI routine completed successfully.
- MPI_ERR_OTHER
- - Other error; use MPI_Error_string to get more information about
this error code.
SEE ALSO¶
MPI_Trace_on, mpirun
LOCATION¶
mpil_trace.c