On Aug 4, 2008, at 9:40 AM, Jeff Squyres wrote:
On Aug 2, 2008, at 2:34 PM, Brian Barrett wrote:
I am curious how all of the above affects client/server or spawned
jobs. If you finalize a BTL then do a connect to a process that
would use that BTL would it reinitialize itself?
To deal with all the dynamics issues, I wouldn't finalized the BTL.
The BML should handle the progress stuff, just as if the add_procs
succeeded but returned no active peers. But I'd guess that's part
of the bit that doesn't work today. I would further suspect that a
BTL will need to have a working progress function in the face of
add_procs failures to cope with all the dynamics options. I'm
travelling this weekend, so I can't verify any of this at the moment.
This seems a little different than the rest of the code base --
we're talking about having the BTL return an error but have the
upper level not treat it as a fatal error.
I think we actually have a few different situations ("fail" means
"not returning OMPI_SUCCESS"):
1. btl component init fails (only during MPI_INIT): the API supports
no notion of failure -- it either returns modules or not (i.e.,
valid pointers or NULL). If NULL is returned, the component is
ignored and unloaded.
2. btl add_procs during MPI_INIT fails: this is under debate
3. btl add_procs during MPI-2 dynamics fails: this is under debate
For #2 and #3, I suspect that only the BTL knows if it can continue
or not. For example, a failure in #3 may cause the entire BTL to be
hosed such that it can no longer communicate with procs that it
previously successfully added (e.g., in MPI_INIT). So we really
need add_procs to be able to return multiple things:
A. OMPI_SUCCESS / all was good
B. a non-fatal error occurred such that this BTL cannot communicate
with the desired peers, but the upper level PML can continue
C. a fatal error has occurred such that the upper level should abort
(or, more specifically, do whatever the error manager says)
I think that for B in both #2 and #3, we can just have the BTL set
all the reachability bits to 0 and return OMPI_SUCCESS. But for C,
the BTL should return != OMPI_SUCCESS. The PML should treat it as a
fatal error and therefore call the error manager.
I think that this is in-line with Brian's original comments, right?
I suppose, but that's a pain when you just want to say "I don't
support calling add_procs a second time" :). But I'm not going to fix
all the BTLs to make that work right, so I suppose in the end I really
don't have a strong opinion.
Brian
