I have had a similar load related problem with Bcast. I don't know what caused it though. With this one, what about the possibility of a buffer overrun or network saturation?
--- On Tue, 24/8/10, Richard Treumann <treumann_at_[hidden]> wrote:
From: Richard Treumann <treumann_at_[hidden]>
Subject: Re: [OMPI users] IMB-MPI broadcast test stalls for large core counts: debug ideas?
To: "Open MPI Users" <users_at_[hidden]>
Received: Tuesday, 24 August, 2010, 9:39 AM
It is hard to imagine how a total data
load of 41,943,040 bytes could be a problem. That
is really not much data. By the time the BCAST is done, each task (except
root) will have received a single half meg message form one sender. That
is not much.
IMB does shift the root so some tasks may be in iteration
9 while some are still in iteration 8 or 7 but a 1/2 meg message should
use rendezvous protocol so no message will be injected into the network
until the destination task is ready to receive it.
Any task can be in only one MPI_Bcast at a time so
the total active data cannot ever exceed the 41,943,040 bytes, no matter
how fast the MPI_Bcast loop tries to iterate.
(There are MPI_Bcast algorithms that chunk the data
into smaller messages but even with those algorithms, the total concurrent
load will not exceed 41,943,040 bytes.)
Dick Treumann - MPI Team
users-bounces_at_[hidden] wrote on 08/23/2010 05:09:56
> On Sun, Aug 22, 2010 at 9:57 PM, Randolph Pullen
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