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Subject: Re: [OMPI users] 3.5 seconds before application launches
From: doriankrause (doriankrause_at_[hidden])
Date: 2009-02-25 16:01:55


Vittorio wrote:
> Hi!
> I'm using OpenMPI 1.3 on two nodes connected with Infiniband; i'm using
> Gentoo Linux x86_64.
>
> I've noticed that before any application starts there is a variable amount
> of time (around 3.5 seconds) in which the terminal just hangs with no output
> and then the application starts and works well.
>
> I imagined that there might have been some initialization routine somewhere
> in the Infiniband layer or in the software stack, but as i continued my
> tests i observed that this "latency" time is not present in other MPI
> implementations (like mvapich2) where my application starts immediately (but
> performs worse).
>
> Is my MPI configuration/installation broken or is this expected behaviour?
>

Hi,

I'm not really qualified to answer this question, but I know that in
contrast
to other MPI implementations (MPICH) the modular structure of Open MPI
is based
on shared libs that are dlopened at the startup. As symbol relocation can be
costly this might be a reason why the startup time is higher.

Have you checked wether this is an mpiexec start issue or the MPI_Init call?

Regards,
Dorian

> thanks a lot!
> Vittorio
>
>
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