On May 8, 2008, at 7:50 AM, Jeff Squyres wrote:
FWIW:
- I think "none" is a slightly better word than "null" for this value;
"none" implies that you don't open anything, whereas "null" could be a
specific component (as it is/was in some frameworks).
Calling it 'none' sounds fine to me.
- Whatever word we decide on will need to become a reserved component
name (i.e., no components will be able to use that as their name). We
should adjust autogen.sh and friends to ensure that no component has
this name (not difficult -- just make autogen.sh abort if it finds a
component of this name).
Good idea.
- Is this value supposed to be accessible/usable by users, or is it
meant to only be used internally?
I would say it should be used internally. But I don't know what use
case Ralph was thinking of with this.
There is something to be said for being able to add such an option to
the .openmpi/mca-params.conf file while testing or to an AMCA file
for a particular configuration. So maybe we should expose it. It may
able be useful for debugging problems encountered in the wild.
--> If intended to be used by users, I marginally prefer a single,
lower case, simple word (e.g., "none") vs. a caps word -- it's easier
to type and is consistent with our other values. I recognize that we
don't want users to use the value by accident, and making it all caps
makes it stand out, but I think the consistency issues are more
important.
Keeping it case-consistent with other components is probably a good
thing.
--> If not intended to be used by users (i.e., it's an internal
mechanism only), is there a reason why we're not using a zero-length
string (e.g., mpirun --mca foo "")?
I think a zero length string might get confusing with the empty
string. The empty string is taken to mean auto-select from all
available components, which currently cannot be specified on the
command line as an -mca option. The 0 length string is close and
nearly indistinguishable in an (A)MCA file from a NULL string.
-- Josh
On May 6, 2008, at 2:09 PM, Josh Hursey wrote:
What: Add a MCA-NULL option to open no components in mca_base_open()
Why: Sometimes we do not want to open or select any components of
a framework.
Where: patch attached for current trunk.
When: Needs further discussion.
Timeout: Unknown. [May 13, 2008 (After teleconf)?]
Short Version:
--------------
This RFC is intended to continue discussion on the thread started
here:
http://www.open-mpi.org/community/lists/devel/2008/05/3793.php
Discussion should occur on list, but maybe try to come to some
settlement on this RFC in the next week or two.
Longer Version:
---------------
Currently there is no way to express to the MCA system that
absolutely no components of a framework are needed and therefore
nothing should be opened. The addition of a sentinel value is needed
to explicitly express this intention. It was suggested that if a
'MCA-NULL' value is passed as an argument for a framework then this
should be taken to indicate such an intention.
<mca-null.diff>
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Jeff Squyres
Cisco Systems
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