The checkpoint/restart work that I have integrated does not respond
to
failure at the moment. If a failures happens I want ORTE to terminate
the entire job. I will then restart the entire job from a checkpoint
file. This follows the 'all fall down' approach that users typically
expect when using a global C/R technique.
Eventually I want to integrate something better where I can respond
to
a failure with a recovery from inside ORTE. I'm not there yet, but
hopefully in the near future.
I'll let the UTK group talk about what they are doing with ORTE,
but I
suspect they will be taking advantage of the errmgr to help respond
to
failure and restart a single process.
It is important to consider in this context that we do *not* always
want ORTE to abort whenever it detects a process failure. This is the
default mode for MPI applications (MPI_ERRORS_ARE_FATAL), and should
be supported. But there is another mode in which we would like ORTE
to
keep running to conform with (MPI_ERRORS_RETURN):
http://www.mpi-forum.org/docs/mpi-11-html/node148.html
It is known that certain standards conformant MPI "fault tolerant"
programs do not work in Open MPI for various reasons some in the
runtime and some external. Here we are mostly talking about
disconnected fates of intra-communicator groups. I have a test in the
ompi-tests repository that illustrates this problem, but I do not
have
time to fix it at the moment.
So in short keep the errmgr around for now. I suspect we will be
using
it, and possibly tweaking it in the nearish future.
Thanks for the observation.
Cheers,
Josh
On Mar 6, 2008, at 10:44 AM, Ralph Castain wrote:
Hello
I've been doing some work on fault response within the system, and
finally
realized something I should probably have seen awhile back. Perhaps
I am
misunderstanding somewhere, so forgive the ignorance if so.
When we designed ORTE some time in the deep, dark past, we had
envisioned
that people might want multiple ways of responding to process faults
and/or
abnormal terminations. You might want to just abort the job, attempt
to
restart just that proc, attempt to restart the job, etc. To support
these
multiple options, and to provide a means for people to simply try
new ones,
we created the errmgr framework.
Our thought was that a process and/or daemon would call the errmgr
when we
detected something abnormal happening, and that the selected errmgr
component could then do whatever fault response was desired.
However, I now see that the fault tolerance mechanisms inside of
OMPI do not
seem to be using that methodology. Instead, we have hard-coded a
particular
response into the system.
If we configure without FT, we just abort the entire job since that
is the
only errmgr component that exists.
If we configure with FT, then we execute the hard-coded C/R
methodology.
This is built directly into the code, so there is no option as to
what
happens.
Is there a reason why the errmgr framework was not used? Did the FT
team
decide that this was not a useful tool to support multiple FT
strategies?
Can we modify it to better serve those needs, or is it simply not
feasible?
If it isn't going to be used for that purpose, then I might as well
remove
it. As things stand, there really is no purpose served by the errmgr
framework - might as well replace it with just a function call.
Appreciate any insights
Ralph
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