| A.3. Sampling of MPI Applications | ||
|---|---|---|
 | Appendix A. Sampling MPI Applications |  |
| A.3. Sampling of MPI Applications | ||
|---|---|---|
| | Appendix A. Sampling MPI Applications | |
When sampling a normal, non-MPI application,
the sample command creates a fingerprint
file called sample.smp by default, unless
overridden by an explicit parameter like so:
$ sample -o myapp-test4.smp -r ./myapp arg1
In a MPI environment, there are several instances of the sampler that all try to create their own fingerprint files, typically in the same directory. Clearly, they need to use different names for their files, or else the files overwrite one another. It is your responsibility to provide a template for the names of these files as an input to the sample command:
$ mpirun -np 16 sample -o test4/myapp-%r.smp -r ./myapp arg1
The %r is a special sequence that expands to
a unique value for each rank. On many systems it expands to the
MPI rank number, but on systems where the rank number is not
available to Freja, it expands to a combination of hostname
and a unique number, e.g., "node45-17",
where node45 is the name of the node,
and 17 is a sequential number within that
node.
The following table lists the special sequences that Freja recognizes:
Table A.1. Fingerprint filename substitutions
| Sequence | Substitution |
|---|---|
| %r | If executed in an MPI environment this is replaced with the MPI rank number, if known. On other systems it is equivalent to %h-%p (see below). Example: x-%r.smp becomes x-17.smp (MPI), or x-myhost-123.smp (otherwise) |
| %h | Replaced with the current hostname of the machine. Example: x-%h.smp becomes x-myhost.smp |
| %p | Replaced with a unique number within the current host. Note: It is not related to the Pid of the target process. Example: x-%p.smp becomes x-123.smp |
| %u | Expands to
". Example: x%u.smp becomes x.smp (first file), x.1.smp (next file) etc. |
| %U | Expands to
". Example: x%U.smp becomes x.0.smp (first file), x.1.smp (next file), etc. |
%{ENV} | Replaced with the content of the environment
variable Example: x-%{USER}.smp becomes x-demo.smp |
| %% | Replaced with a single %. This is sometimes useful on Windows when encoding commands in a batch file. Example: x%%.smp becomes x%.smp |
The following table lists the environment variables that Freja tries in sequence to determine the MPI rank number.
Table A.2. %r substitutions
| Environment variable[a] | Used for MPI type: |
|---|---|
| PMI_RANK | MPICH 2 and derivatives |
| OMPI_COMM_WORLD_RANK | OpenMPI 1.3 |
| OMPI_MCA_ns_nds_vpid | OpenMPI 1.2 and derivatives |
| PMI_ID | SLURM PMI |
| SLURM_PROCID | SLURM |
| LAMRANK | LAM |
| MPI_RANKID | HP MPI for Linux |
| MP_CHILD | IBM PE |
| MP_RANK | Sun CT |
| MPIRUN_RANK | MVAPICH 1.1 |
[a] The inclusion of an environment variable in this list does not automatically imply that Freja is certified for that platform. | |
| |  | |
| A.2. Scope |  | A.4. Alternative method: wrapper scripts |