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Subject: Re: [OMPI users] OpenMPI at scale on Cray XK7
From: Nathan Hjelm (hjelmn_at_[hidden])
Date: 2013-04-23 13:09:17

On Tue, Apr 23, 2013 at 12:21:49PM +0400, ???????????????????? ???????????? wrote:
> Hi,
> Nathan, could you please advise what is expected startup time for OpenMPI
> job at such scale (128K ranks)? I'm interesting in
> 1) time from mpirun start to completion of MPI_Init()

It takes less than a minute to run:

mpirun -n 131072 /bin/true

> 2) time from MPI_Init() start to completion of MPI_Init()

A simple MPI application took about about 1.25 mins to run. If you want to see our setup you can take a look at contrib/platform/lanl/cray_xe6.

> >From my experience for 52800 rank job
> 1) took around 20 min
> 2) took around 12 min
> that actually looks like a hung.

How many nodes? I have never seen launch times that bad on Cielo. You could try adding -mca routed debruijn -novm and see if that helps. It will reduce the amount of communication between compute nodes and the login node.

> Any advice how to improve startup times of large scale jobs would be very
> much appreciated.

The bottleneck for launching at scale is the initial communication between the orteds and mpirun. At this time I don't know what can be done to improve that (I have some ideas but nothing has been implemented yet). At 8192 nodes this takes less than a minute. Everything else should be fairly quick.

-Nathan Hjelm