326. Miscellaneous Control of Profiling
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There is a clear requirement for the user code to be able to control
the profiler dynamically at run time. This capability is normally used for (at
least) the purposes of
- Enabling and disabling profiling depending on the state of the
calculation.
- Flushing trace buffers at non-critical points in the calculation.
- Adding user events to a trace file.
These requirements are met by use of MPI_PCONTROL.
| MPI_PCONTROL(level, ...) |
| IN level | Profiling level (integer) |
int MPI_Pcontrol(const int level, ...)
MPI_Pcontrol(level)
INTEGER, INTENT(IN) :: level
MPI_PCONTROL(LEVEL)
INTEGER LEVEL
MPI libraries themselves make no use of this routine, and simply
return immediately to the user code. However the presence of calls to
this routine allows a profiling package to be explicitly called by the
user.
Since MPI has no control of the implementation of the profiling code,
we are unable to specify precisely the semantics
that
will be
provided by calls to MPI_PCONTROL. This vagueness extends to the
number of arguments to the function, and their datatypes.
However to provide some level of portability of user codes to different
profiling libraries, we request the following meanings for certain
values of level.
- level==0
Profiling is disabled.
- level==1
Profiling is enabled at a normal default level of detail.
- level==2
Profile buffers are flushed, which may be a no-op in some profilers.
- All other values of level
have profile library defined effects and additional arguments.
We also request that the default state after MPI_INIT has been
called is for profiling to be enabled at the normal default level.
(i.e., as if MPI_PCONTROL had just been called with the
argument 1). This allows users to link with a profiling library and
to obtain profile output without having to modify their source code at
all.
The provision of MPI_PCONTROL as a no-op in the standard MPI
library supports the collection of more
detailed profiling information with source
code that can still link against the standard MPI library.
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