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4–Running MPI on QLogic Adapters

Open MPI

IB0054606-02 A 4-7

For Fortran 90 programs:

$ mpif90 -f90=pgf90 -show pi3f90.f90 -o pi3f90

pgf90 -I/usr/include/mpich/pgi5/x86_64 -c -I/usr/include

pi3f90.f90 -c

pgf90 pi3f90.o -o pi3f90 -lmpichf90 -lmpich

-lmpichabiglue_pgi5

Fortran 95 programs will be similar to the above.

For C programs:

$ mpicc -cc=pgcc -show cpi.c

pgcc -c cpi.c

pgcc cpi.o -lmpich -lpgftnrtl -lmpichabiglue_pgi5

Compiler and Linker Variables

When you use environment variables (e.g., $MPICH_CC) to select the compiler

mpicc (and others) will use, the scripts will also set the matching linker variable

(for example, $MPICH_CLINKER), if it is not already set. When both the

environment variable and command line options are used (-cc=gcc), the

command line variable is used.

When both the compiler and linker variables are set, and they do not match for the

compiler you are using, the MPI program may fail to link; or, if it links, it may not

execute correctly.

Process Allocation

Normally MPI jobs are run with each node program (process) being associated

with a dedicated QLogic IB adapter hardware context that is mapped to a CPU.

If the number of node programs is greater than the available number of hardware

contexts, software context sharing increases the number of node programs that

can be run. Each adapter supports four software contexts per hardware context,

so up to four node programs (from the same MPI job) can share that hardware

context. There is a small additional overhead for each shared context.

Table 4-5 shows the maximum number of contexts available for each adapter.

1 2 ... 74 75 76 77 78 79 80 81 82 83 84 ... 283 284

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