On Feb 24, 2017, at 10:11 AM, Dahai Guo <dahaiguo2...@yahoo.com> wrote:
>
> oops, I should use the word "MCA parameters". If I define a MCA parameter
> (apath, for example) in etc/openmpi-mca-params.conf, how can function
> setup_fork in ompi/orte/mca/schizo/ompi/schizo_ompi.c get its value? I tried
> to call getenv("apath") there, which return null.
Settings MCA parameters does not necessarily set environment variables. More
below.
> However, If I defined it in the cmd line, mpirun -mca apath=sth .., then I
> could get it in setup_fork.
There are multiple mechanisms in which MCA params are passed to the back-end
MPI processes.
1. If they are set via "--mca a b" on the mpirun command line, they are passed
back to the launching orteds as part of the launch schema for the job. I.e.,
the MCA param names and values are bundled up and sent in the network message
to each of the orteds that are involved in the launching of the target
processes. IIRC, the launching orteds will fork, setenv a corresponding
environment variable for each of the MCA param values in the launch schema, and
then exec the MPI process. The MPI process then picks up those MCA param
values from the environment variables.
2. If they are set via the openmpi-mca-params.conf file, they are not sent via
network message in the launch schema. Instead, each Open MPI process
(including MPI processes and orteds) reads that file upon startup to get the
values (more specifically: all Open MPI processes *always* read this file
before processing whatever MCA param values are sent in the launch schema). A
consequence: if openmpi-mca-params.conf is not on a network filesystem (and
visible to all Open MPI processes on all servers), you need to copy the change
you made to the one openmpi-mca-params.conf file to all copies of
openmpi-mca-params.conf.
-----
What are you trying to do?
If you're working in an MPI application, you can use the MPI_T API to retrieve
MCA parameter names and their current values (regardless of whether mechanism
#1 or #2 -- or another mechanism -- is used).
If you're working in the Open MPI code base, you should be using the internal
opal_mca_var API to retrieve and/or set MCA param values. See
https://github.com/open-mpi/ompi/blob/master/opal/mca/base/mca_base_var.h for
all the functions available in this API.
--
Jeff Squyres
jsquy...@cisco.com
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