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Subject: Re: [OMPI devel] Deadlock on openib when using hindexed types
From: Rolf Vandevaart (Rolf.Vandevaart_at_[hidden])
Date: 2009-09-04 07:59:13

I think you are running into a bug that we saw also and we recently
fixed. We would see a hang when we were sending from a contiguous type
to a non-contiguous type using a single port over openib. The problem
was that the state of the request on the sending side was not being
properly updated in that case. The reason we see it with only one port
vs two is because different protocols are used depending on the number
of ports.

Don Kerr found and fixed the problem in both the trunk and the branch.

1.3 Branch:

If you are running the latest bits and still seeing the problem, then I
guess it is something else.


On 09/04/09 04:40, Sylvain Jeaugey wrote:
> Hi all,
> We're currently working with romio and we hit a problem when exchanging
> data with hindexed types with the openib btl.
> The attached reproducer (adapted from romio) is working fine on tcp,
> blocks on openib when using 1 port but works if we use 2 ports (!). I
> tested it against the trunk and the 1.3.3 release with the same
> conclusions.
> The basic idea is : processes 0..3 send contiguous data to process 0. 0
> receives these buffers with an hindexed datatype which scatters data at
> different offsets.
> Receiving in a contiguous manner works, but receiving with an hindexed
> datatype makes the remote sends block. Yes, the remote send, not the
> receive. The receive is working fine and data is correctly scattered on
> the buffer, but the senders on the other node are stuck in the Wait().
> I tried not using MPI_BOTTOM, which changed nothing. It seems that the
> problem only occurs when STRIPE*NB (the size of the send) is higher than
> 12k -namely the RDMA threshold- but I didn't manage to remove the
> deadlock by increasing the RDMA threshold.
> I've tried to do some debugging, but I'm a bit lost on where the
> non-contiguous types are handled and how they affect btl communication.
> So, if anyone has a clue on where I should look at, I'm interested !
> Thanks,
> Sylvain
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