Re: [OMPI users] openmpi credits for eager messages

[George Bosilca]

Well ... this is exactly the kind of behavior a high performance application try to achieve isn't it ?

  Thanks,
    George.

On Feb 1, 2008, at 6:32 PM, 8mj6tc...@sneakemail.com wrote:

The problem here is not the flow control. What you need is to avoid buffering the messages on the receiver side. Luckily, Open MPI is entirely configurable at runtime, so this situation is really easy to deal with even at the user level. Set the eager size to zero, and no buffering on the receiver side will be made. Your program will survive as long as there is some available memory on the receiver.

That would make sense. I able to break OpenMPI by having Node A wait for

messages from Node B. Node B is in fact sleeping while Node C bombards
Node A with a few thousand messages. After a while Node B wakes up and

been buried and seg faults. If I decrease the number of messages C is

dig up the test and try again if anyone is seriously curious).


have any clever buffer management) but it didn't crash.

Sacerdoti, Federico Federico.Sacerdoti-at-deshaw.com
|openmpi-users/Allow| wrote:

sends Node A the message it's been waiting on, but Node A has long since sending, it works properly. This was on OpenMPI 1.2.4 (using I think the SM BTL (might have been MX or TCP, but certainly not infiniband. I could Trying the same test on MPICH/MX went very very slow (I don't think they

Hi,

I am readying an openmpi 1.2.5 software stack for use with a
many-thousand core cluster. I have a question about sending small
messages that I hope can be answered on this list.

I was under the impression that if node A wants to send a small MPI

that B has enough buffer space to accept the message. Credits are
required by the mpi layer regardless of the BTL transport layer used.


is not an openmpi feature.

Thanks,
Federico

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message to node B, it must have a credit to do so. The credit assures A I have been told by a Voltaire tech that this is not so, the credits are used by the infiniband transport layer to reliably send a message, and

--
--Kris

叶ってしまう夢は本当の夢と言えん。
[A dream that comes true can't really be called a dream.]
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