Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: Re: [OMPI users] OpenMP + OpenMPI
From: Durga Choudhury (dpchoudh_at_[hidden])
Date: 2007-12-06 09:54:22


Automatically striping large messages across multiple NICs is certainly a
very nice feature; I was not aware that OpenMPI does this transparently. (I
wonder if other MPI implementations do this or not). However, I have the
following concern: Since the communication over an ethernet NIC is most
likely over IP, does it take into account the route cost when striping
messages? For example, host A and B in the MPD ring might be connected via
two NICs, one direct and one via an intermediate router, or one with a large
bandwidth and another with a small bandwidth. Does OpenMPI send a smaller
chunk of data over a route with a higher cost?

Because of this concern, I think the channel bonding approach someone else
suggested is more preferable; all these details will be taken care of at the
hardware level instead of at the IP level.
Thanks
Durga

On Dec 6, 2007 9:42 AM, Jeff Squyres <jsquyres_at_[hidden]> wrote:

> Wow, that's quite a .sig. :-)
>
> Open MPI will automatically stripe large messages across however many
> NICs you have. So you shouldn't need to use multiple threads.
>
> The threading support in the OMPI v1.2 series is broken; it's not
> worth using. There's a big warning in configure when you enable it. :-)
>
>
> On Dec 5, 2007, at 9:57 PM, Tee Wen Kai wrote:
>
> > Hi everyone,
> >
> > I have installed openmpi-1.2.3. My system has two ethernet ports.
> > Thus, I am trying to make use of both ports to speed up the
> > communication process by using openmp to split into two threads.
> > However, this implementation always cause error. Then I realized
> > that I need to build openmpi using --enable-mpi-threads and use
> > MPI_Init_thread to initialize. But, the initialization always return
> > MPI_THREAD_SINGLE no matter what value I set. Using ompi_info|grep
> > Thread, it shows that thread support has already been activated.
> > Thus, I seek your help to teach me what other configurations I need
> > to set in order to use multi-threads and what are the parameters to
> > include in mpirun in order to use the two ethernet ports.
> >
> > Thank you very much.
> >
> > Regards,
> > Tee
> >
> >
> >
> > _________________________________________________
> >
> >
> >
> > Many of us spend our time wishing for things we could have if we
> > didn't spend half our time wishing.
> >
> > Looking for last minute shopping deals? Find them fast with Yahoo!
> > Search._______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
> --
> Jeff Squyres
> Cisco Systems
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>

-- 
Its a battle between humans and communists;
Which side are you in?
.