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Subject: Re: [OMPI users] Debugging memory use of Open MPI
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2009-04-14 14:12:18


Shaun Jackman wrote:

> Eugene Loh wrote:
>
>> At 2500 bytes, all messages will presumably be sent "eagerly" --
>> without waiting for the receiver to indicate that it's ready to
>> receive that particular message. This would suggest congestion, if
>> any, is on the receiver side. Some kind of congestion could, I
>> suppose, still occur and back up on the sender side.
>
> Can anyone chime in as to what the message size limit is for an
> `eager' transmission?

ompi_info -a | grep eager
depends on the BTL. E.g., sm=4K but tcp is 64K. self is 128K.

>> On the other hand, I assume the memory imbalance we're talking about
>> is rather severe. Much more than 2500 bytes to be noticeable, I
>> would think. Is that really the situation you're imagining?
>
> The memory imbalance is drastic. I'm expecting 2 GB of memory use per
> process. The heaving processes (13/16) use the expected amount of
> memory; the remainder (3/16) misbehaving processes use more than twice
> as much memory. The specifics vary from run to run of course. So, yes,
> there is gigs of unexpected memory use to track down.

Umm, how big of a message imbalance do you think you might have? (The
inflection in my voice doesn't come out well in e-mail.) Anyhow, that
sounds like, um, "lots" of 2500-byte messages.