Attached is the message list for rank 0 for the communication step that is failing. There are about 160 isends and irecvs. The ‘message size’ is actually
a number of cells. On some steps only one 8-byte word per cell is communicated, at another step we exchange 7 words, and another step we exchange 21 words. You can see the smallest is 10 cells, the largest around 1000 cells.
Thus for the 7-word communication step, the smallest messages are 560 bytes, the largest are 56000 bytes, and there is a distribution of sizes. For the single-word
communication step, the size distribution would be from 80 bytes to 8000 and for the 21-word step it would be from 1680 to 168000 bytes.
From: email@example.com [mailto:firstname.lastname@example.org]
On Behalf Of Rolf vandeVaart
Sent: Thursday, June 27, 2013 9:02 AM
To: Open MPI Users
Subject: EXTERNAL: Re: [OMPI users] Application hangs on mpi_waitall
Ed, how large are the messages that you are sending and receiving?
It ran a bit longer but still deadlocked. All matching sends are posted 1:1with posted recvs so it is a delivery issue of some kind. I'm running a debug compiled version tonight to see what that might turn up. I may try to rewrite with
blocking sends and see if that works. I can also try adding a barrier (irecvs, barrier, isends, waitall) to make sure sends are not buffering waiting for recvs to be posted.
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-------- Original message --------
From: George Bosilca <email@example.com>
To: Open MPI Users <firstname.lastname@example.org>
Subject: Re: [OMPI users] Application hangs on mpi_waitall
Im not sure but there might be a case where the BTL is getting overwhelmed by the nob-blocking operations while trying to setup the connection. There is a simple test for this. Add an MPI_Alltoall with a reasonable size (100k) before you start posting the non-blocking
receives, and let's see if this solves your issue.
On Jun 26, 2013, at 04:02 , email@example.com wrote:
> An update: I recoded the mpi_waitall as a loop over the requests with
> mpi_test and a 30 second timeout. The timeout happens unpredictably,
> sometimes after 10 minutes of run time, other times after 15 minutes, for
> the exact same case.
> After 30 seconds, I print out the status of all outstanding receive
> requests. The message tags that are outstanding have definitely been
> sent, so I am wondering why they are not getting received?
> As I said before, everybody posts non-blocking standard receives, then
> non-blocking standard sends, then calls mpi_waitall. Each process is
> typically waiting on 200 to 300 requests. Is deadlock possible via this
> implementation approach under some kind of unusual conditions?
> Thanks again,
>> I'm running OpenMPI 1.6.4 and seeing a problem where mpi_waitall never
>> returns. The case runs fine with MVAPICH. The logic associated with the
>> communications has been extensively debugged in the past; we don't think
>> it has errors. Each process posts non-blocking receives, non-blocking
>> sends, and then does waitall on all the outstanding requests.
>> The work is broken down into 960 chunks. If I run with 960 processes (60
>> nodes of 16 cores each), things seem to work. If I use 160 processes
>> (each process handling 6 chunks of work), then each process is handling 6
>> times as much communication, and that is the case that hangs with OpenMPI
>> 1.6.4; again, seems to work with MVAPICH. Is there an obvious place to
>> start, diagnostically? We're using the openib btl.
>> users mailing list
> users mailing list
users mailing list
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