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Subject: Re: [OMPI users] Strange "All-to-All" behavior
From: Sebastian Rettenberger (rettenbs_at_[hidden])
Date: 2013-04-28 06:10:46


Hi,

hast du das Problem nur mit OpenMPI oder auch mit anderen MPI Bibliotheken
(z.B. MPICH2)

Ansonsten kannst du auch mal probieren, ob du das All-to-all mit Collectives
hin bekommst, z.B. Scatter oder Gatter.

Viele Grüße
Sebastian

> Hi,
>
> I have encountered really bad performance when all the nodes send data
> to all the other nodes. I use Isend and Irecv with multiple
> outstanding sends per node. I debugged the behavior and came to the
> following conclusion: It seems that one sender locks out all other
> senders for one receiver. This sender releases the receiver only when
> there are no more sends posted or a node with lower rank, wants to
> send to this node (deadlock prevention). As a consequence, node 0
> sends all its data to all nodes, while all others are waiting, then
> node 1 sends all the data, …
>
> What is the rationale behind this behaviour and can I change it by
> some MCA parameter?
>
> Thanks
>
> Stephan
>
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