I am now ok with the env. var. Pretty simple to set and get into the code to pack the messages.
About tests, it is so dependent on the cluster, OpenMPI itself and the model, this way is not an industrial way of tuning the computation. But the env. var. is a good workaround.

Thanks again to all of you for the help.
Best regards,

On 12/16/2010 06:21 PM, Eugene Loh wrote:
Jeff Squyres wrote:
On Dec 16, 2010, at 5:14 AM, Mathieu Gontier wrote:
We have lead some tests and the option btl_sm_eager_limit has a positive consequence on the performance. Eugene, thank you for your links.
Just be aware of the tradeoff you're making: space for time.
Now, to offer a good support to our users, we would like to get the value of this parameters at the runtime. I am aware I can have the value running ompi_info like following:
ompi_info --param btl all | grep btl_sm_eager_limit

but can I get the value during the computation when I run mpirun -np 12 --mca btl_sm_eager_limit 8192 my_binary? This value could be compared with the buffer size into my code and some warning put into the output.
We don't currently have a user-exposed method of retrieving MCA parameter values.  As you noted in your 2nd email, if the value was set by setting an environment variable, then you can just getenv() it.  But if the value was set some other way (e.g., via a file), it won't necessarily be loaded in the environment.
If you are desperate to get this value, I suppose you could run empirical tests within your application.  This would be a little ugly, but could work well enough if you are desperate enough.
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