Why would this patch result in zombied processes and poor cleanup? When ORTE receive notification of a process terminating/aborting then it triggers the termination of the job (without UTK's RFC) which should ensure a clean shutdown. This patch just tells ORTE that a few other processes should be the first to die, which will trigger the same response in ORTE.
I guess I'm unclear about this concern since it should be a concern in the current ORTE as well then. I agree that it will be a concern once we have the OMPI layer handling error management triggered off of a callback, but that is a different RFC. Something that might help those listening to this thread. The current behavior of MPI_Abort in OMPI results in the semantics of: -------------- internal_MPI_Abort(MPI_COMM_SELF, exit_code) -------------- regardless of the communicator actually passed to the MPI_Abort at the application level. It should be: -------------- internal_MPI_Abort(comm_provided, exit_code) -------------- Semantically, this patch just makes the group actually being aborted match the communicator provided. In practicality, the job will terminate when any process in the job calls abort - so the result (in todays codebase) will be the same. -- Josh On Fri, Jun 10, 2011 at 7:30 AM, Ralph Castain <r...@open-mpi.org> wrote: > I have no issue with uncommenting the code. However, I do see a future > littered with lots of zombied processes and complaints over poor cleanup > again.... > > > On Jun 9, 2011, at 6:08 PM, Joshua Hursey wrote: > >> Ah I see what you are getting at now. >> >> The construction of the list of connected processes is something I, >> intentionally, did not modify from the current Open MPI code. The list is >> calculated based on the locally known set of local and remote process groups >> attached to the communicator. So this is the set of directly connected >> processes in the specified communicator known to the calling process at the >> OMPI level. >> >> ORTE is asked to abort this defined set of processes. Once those processes >> are terminated then ORTE needs to eventually inform all of the processes (in >> the jobid(s) specified - maybe other jobids too?) that these processes have >> failed/aborted. Upon notification of the failed/aborted processes the local >> process (at the OMPI level) needs to determine if that process loss is >> critical based upon the error handlers attached to communicators that it >> shares with the failed/aborted processes. That should be handled in the >> callback from the errmgr at the OMPI level, since connectedness is an MPI >> construct. If the process failure/abort is critical to the local process, >> then upon notification the local process can call abort on the communicator >> effected. >> >> So this has the possibility for a rolling abort effect [the abort of one >> communicator triggers the abort of another due to MPI_ERR_ARE_FATAL]. From >> which (depending upon the error handlers at the user level) the system will >> eventually converge to either some stable subset of process or all processes >> aborting resulting in job termination. >> >> The rolling abort effect relies heavily upon the ability of the runtime to >> make sure that all process failures/abort are eventually known to all alive >> processes. Since all alive processes will know of the failure/abort, it can >> then determine if they are transitively effected by the failure based upon >> the local list of communicators and associated error handlers. But to >> complete this aspect of the abort procedure, we do need the callback >> mechanism from the runtime - but since ORTE (today) will kill the job for >> OMPI then it is not a big deal for end users since the job will terminate >> anyway. Once we have the callback, then we can finish tightening up the OMPI >> layer code. >> >> It is not perfect, but I think it does address the transitive nature of the >> connectivity of MPI processes by relying on the runtime to provide uniform >> notification of failures. I figure that we will need to look over this code >> again and verify that the implementation of MPI_Comm_disconnect and >> associated underpinnings do the 'right thing' with regard to updating the >> communicator structures. But I think that is best addressed as a second set >> of patches. >> >> >> The goal of this patch is to put back in functionality that was commented >> out during the last reorganization of the errmgr. What will likely follow, >> once we have notification of failure/abort at the OMPI level, is a cleanup >> of the connected groups code paths. >> >> >> -- Josh >> >> >> On Jun 9, 2011, at 6:13 PM, George Bosilca wrote: >> >>> What I'm saying is that there is no reason to have any other type of >>> MPI_Abort if we are not able to compute the set of connected processes. >>> >>> With this RFC the processes on the communicator on MPI_Abort will abort. >>> Then the other processes in the same MPI_COMM_WORLD (in fact jobid) will be >>> notified (if we suppose that the ORTE will not make a difference between >>> aborted and faulty). As a result the entire MPI_COMM_WORLD will be aborted, >>> if we consider a sane application where everyone use the same type of error >>> handler. However, this is not enough. We have to distribute the abort >>> signal to every other process "connected", and I don't see how we can >>> compute this list of connected processes in Open MPI today.It is not that I >>> don't see it in your patch, it is that the definition of the connectivity >>> in the MPI standard is transitive and relies heavily on a correct >>> implementation for the MPI_Comm_disconnect. >>> >>> george. >>> >>> On Jun 9, 2011, at 16:59 , Josh Hursey wrote: >>> >>>> On Thu, Jun 9, 2011 at 4:47 PM, George Bosilca <bosi...@eecs.utk.edu> >>>> wrote: >>>>> If this change the behavior of MPI_Abort to only abort processes on the >>>>> specified communicator how this doesn't affects the default user >>>>> experience (when today it aborts everything)? >>>> >>>> Open MPI does abort everything by default - decided by the runtime at >>>> the moment (but addressed in your RFC). So it does not matter if one >>>> process aborts or if many do. So the behavior of MPI_Abort experienced >>>> by the user will not change. Effectively the only change is an extra >>>> message in the runtime before the process actually calls >>>> errmgr.abort(). >>>> >>>> This branch just makes the implementation complete by first telling >>>> ORTE that a group of processes, defined by the communicator, should be >>>> terminated along with the calling process. Currently ORTE notices that >>>> there was an abort, and terminates the job. Once your RFC goes through >>>> then this may no longer be the case, and OMPI can determine what to do >>>> when it receives a process failure notification. >>>> >>>>> >>>>> If we accept the fact that MPI_Abort will only abort the processes in the >>>>> current communicator what happens with the other processes in the same >>>>> MPI_COMM_WORLD (but not on the communicator that has been used by >>>>> MPI_Abort)? >>>> >>>> Currently, ORTE will abort them as well. When your RFC goes through >>>> then the OMPI layer will be notified of the error and can take the >>>> appropriate action, as determined by the MPI standard. >>>> >>>>> What about all the other connected processes (based on the connectivity >>>>> as defined in the MPI standard in Section 10.5.4) ? Do they see this as a >>>>> fault? >>>> >>>> They are informed of the fault via the ORTE errmgr callback routine >>>> (that we have an RFC for), and then can take the appropriate action >>>> based on MPI semantics. So we are pushing the decision of the >>>> implication of the fault to the OMPI layer - where it should be. >>>> >>>> >>>> The remainder of the OMPI layer logic for MPI_ERRORS_RETURN and other >>>> connected error management scenarios is not included in this patch >>>> since that depends on there being a callback to the OMPI layer - which >>>> does not exist just yet. So a small patch to wire in the ORTE piece to >>>> allow the OMPI layer to request a set of processes to be terminated - >>>> to more accurately support MPI_Abort semantics. >>>> >>>> Does that answer your questions? >>>> >>>> -- Josh >>>> >>>> >>>>> >>>>> george. >>>>> >>>>> On Jun 9, 2011, at 16:32 , Josh Hursey wrote: >>>>> >>>>>> WHAT: Fix missing code in MPI_Abort >>>>>> >>>>>> WHY: MPI_Abort is missing logic to ask for termination of the process >>>>>> group defined by the communicator >>>>>> >>>>>> WHERE: Mostly orte/mca/errmgr >>>>>> >>>>>> WHEN: Open MPI trunk >>>>>> >>>>>> TIMEOUT: Tuesday, June 14, 2011 (after teleconf) >>>>>> >>>>>> Details: >>>>>> ------------------------------------------- >>>>>> A bitbucket branch is available here (last sync to r24757 of trunk) >>>>>> https://bitbucket.org/jjhursey/ompi-abort/ >>>>>> >>>>>> In the MPI Standard (v2.2) Section 8.7 after the introduction of >>>>>> MPI_Abort, it states: >>>>>> "This routine makes a best attempt to abort all tasks in the group of >>>>>> comm." >>>>>> >>>>>> Open MPI currently only calls orte_errmgr.abort() to abort the calling >>>>>> process itself. The code to ask for the abort of the other processes >>>>>> in the group defined by the communicator is commented out. Since one >>>>>> process calling abort currently causes all processes in the job to >>>>>> abort, it has not been a big deal. However as the group starts >>>>>> exploring better resilience in the OMPI layer (with further support >>>>>> from the ORTE layer) this aspect of MPI_Abort will become more >>>>>> necessary to get right. >>>>>> >>>>>> This branch adds back the logic necessary for a single process calling >>>>>> MPI_Abort to request, from ORTE errmgr, that a defined subgroup of >>>>>> processes be aborted. Once the request is sent to the HNP, the local >>>>>> process then calls abort on itself. The HNP requests that the defined >>>>>> subgroup of processes be terminated using the existing plm mechanisms >>>>>> for doing so. >>>>>> >>>>>> This change has no effect on the current default user experienced >>>>>> behavior of MPI_Abort. >>>>>> >>>>>> -- >>>>>> Joshua Hursey >>>>>> Postdoctoral Research Associate >>>>>> Oak Ridge National Laboratory >>>>>> http://users.nccs.gov/~jjhursey >>>>>> _______________________________________________ >>>>>> devel mailing list >>>>>> de...@open-mpi.org >>>>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel >>>>> >>>>> >>>>> _______________________________________________ >>>>> devel mailing list >>>>> de...@open-mpi.org >>>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel >>>>> >>>>> >>>> >>>> >>>> >>>> -- >>>> Joshua Hursey >>>> Postdoctoral Research Associate >>>> Oak Ridge National Laboratory >>>> http://users.nccs.gov/~jjhursey >>>> >>>> _______________________________________________ >>>> devel mailing list >>>> de...@open-mpi.org >>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel >>> >>> >>> _______________________________________________ >>> devel mailing list >>> de...@open-mpi.org >>> http://www.open-mpi.org/mailman/listinfo.cgi/devel >>> >> >> >> _______________________________________________ >> devel mailing list >> de...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > _______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel > > -- Joshua Hursey Postdoctoral Research Associate Oak Ridge National Laboratory http://users.nccs.gov/~jjhursey
