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Subject: Re: [OMPI devel] some info is not pushed into the dstore
From: Ralph Castain (rhc_at_[hidden])
Date: 2014-05-27 15:51:41


Hmmm...I did some digging, and the best I can tell is that root cause is that the second job ("b" in the test program) is never actually calling connect_accept! This looks like a change may have occurred in Intercomm_create that is causing it to not recognize the need to do so.

Anyone confirm that diagnosis?

FWIW: job 1 clearly receives and has all the required info in the correct places - it is ready to provide it to job 2, if/when job 2 actually calls connect_accept.

On May 27, 2014, at 10:13 AM, Ralph Castain <rhc_at_[hidden]> wrote:

> Hi Gilles
>
> I concur on the typo and fixed it - thanks for catching it. I'll have to look into the problem you reported as it has been fixed in the past, and was working last I checked it. The info required for this 3-way connect/accept is supposed to be in the modex provided by the common communicator.
>
> On May 27, 2014, at 3:51 AM, Gilles Gouaillardet <gilles.gouaillardet_at_[hidden]> wrote:
>
>> Folks,
>>
>> while debugging the dynamic/intercomm_create from the ibm test suite, i found something odd.
>>
>> i ran *without* any batch manager on a VM (one socket and four cpus)
>> mpirun -np 1 ./dynamic/intercomm_create
>>
>> it hangs by default
>> it works with --mca coll ^ml
>>
>> basically :
>> - task 0 spawns task 1
>> - task 0 spawns task 2
>> - a communicator is created for the 3 tasks via MPI_Intercomm_create()
>>
>> MPI_Intercomm_create() calls ompi_comm_get_rprocs() which calls ompi_proc_set_locality()
>>
>> then, on task 1, ompi_proc_set_locality() calls
>> opal_dstore.fetch(opal_dstore_internal, "task 2"->proc_name, ...) which fails and this is OK
>> then
>> opal_dstore_fetch(opal_dstore_nonpeer, "task 2"->proc_name, ...) which fails and this is *not* OK
>>
>> /* on task 2, the first fetch for "task 1" fails but the second success */
>>
>> my analysis is that when task 2 was created, it updated its opal_dstore_nonpeer with info from "task 1" which was previously spawned by task 0.
>> when task 1 was spawned, task 2 did not exist yet and hence opal_dstore_nonpeer contains no reference to task 2.
>> but when task 2 was spawned, opal_dstore_nonpeer of task 1 has not been updated, hence the failure
>>
>> (on task 1, proc_flags of task 2 has incorrect locality, this likely confuses coll ml and hang the test)
>>
>> should task1 have received new information when task 2 was spawned ?
>> shoud task2 have sent information to task1 when it was spawned ?
>> should task1 have (tried to) get fresh information before invoking MPI_Intercomm_create() ?
>>
>> incidentally, i found ompi_proc_set_locality calls opal_dstore.store with
>> identifier &proc (the argument is &proc->proc_name everywhere else, so this
>> is likely a bug/typo. the attached patch fixes this.
>>
>> Thanks in advance for your feedback,
>>
>> Gilles
>> <proc.patch>_______________________________________________
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>