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Subject: Re: [OMPI users] mca_pml_ob1_send blocks
From: Shaun Jackman (sjackman_at_[hidden])
Date: 2009-08-25 18:51:41

Jeff Squyres wrote:
> On Aug 24, 2009, at 2:18 PM, Shaun Jackman wrote:
>> I'm seeing MPI_Send block in mca_pml_ob1_send. The packet is shorter
>> than the eager transmit limit for shared memory (3300 bytes < 4096
>> bytes). I'm trying to determine if MPI_Send is blocking due to a
>> deadlock. Will MPI_Send block even when sending a packet eagerly?
> It can, yes. Message size is one of multiple factors that can cause
> MPI_SEND to block -- so yes, it's even possible for short/eager
> messages to block in MPI_SEND.
> Can you tell if the corresponding receive has already been posted and
> is making progress in the receiver?

Hi Jeff,

The receiver posts a single MPI_Irecv in advance, and as soon as it's
received a message it posts a new MPI_Irecv. However, there are
multiple processes sending to the receiver, and only one MPI_Irecv posted.