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Subject: Re: [OMPI devel] some info is not pushed into the dstore
From: Ralph Castain (rhc_at_[hidden])
Date: 2014-05-28 08:40:55


On May 28, 2014, at 1:18 AM, Gilles Gouaillardet <gilles.gouaillardet_at_[hidden]> wrote:

> i finally got it :-)

Hooray! Thanks for digging deeper.

>
> /* i previously got it "almost" right ... */
>
> here is what happens on job 2 (with trunk) :
> MPI_Intercomm_create calls ompi_comm_get_rprocs that calls ompi_proc_unpack
> => ompi_proc_unpack store job 3 info into opal_dstore_peer
>
>
> then ompi_comm_get_rprocs calls ompi_proc_set_locality(job 3)
> => ompi_proc_set_locality fetch information job 3 info from opal_dstore_internal (not found) and then opal_dstore_nonpeer (not found again) and then fails.
> this is just the consequence of ompi_proc_unpack stored job 3 info in opal_dstore_peer and not in opal_dstore_nonpeer
>
> i do not understand which of opal_dstore_peer and opal_dstore_nonpeer should be used

Neither do I, frankly - all I can do is hope that someone actually uses the requested multi-store capability as it definitely makes it harder to know what should be going where...

> and when, so i wrote a defensive patch (fetch both opal_dstore_nonpeer and then opal_dstore_peer if not previously found).
>
> please someone review this and comment/fix it if needed
> (for example, store in opal_dstore_nonpeer instead of opal_dstore_peer
> *or*
> fetch in opal_dstore_peer instead of opal_dstore_nonpeer
> and/or something else )

It looks fine as written - again, thanks for finding it.

>
> and then, locality is correctly set, coll ml receives correct information and this does not
> hang any more if mpirun is invoked without --mca coll ^ml and on a single node single socket VM)
>
> bottom line, job 2 *did* receive information of job 3 but failed to store/fetch it in the right opal_store !
>
> v1.8 is unaffected since there is only one dstore
>
> Cheers,
>
> Gilles
>
>
> On Wed, May 28, 2014 at 4:51 AM, Ralph Castain <rhc_at_[hidden]> wrote:
> 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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> >
>
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