On Jun 10, 2011, at 6:48 AM, Josh Hursey wrote: > 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.
My comment was to "the future" - i.e., looking to the point where we get layered, rolling aborts. I agree that this specific RFC won't change the current behavior, and as I said, I have no issue with it. > > > 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 > > _______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel
