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Subject: Re: [OMPI users] openmpi shared memory feature
From: Ralph Castain (rhc_at_[hidden])
Date: 2012-10-27 12:53:31


On Oct 27, 2012, at 9:47 AM, Mahmood Naderan <nt_mahmood_at_[hidden]> wrote:

>
> >Because communicating through shared memory when sending messages between processes on the same server is far faster than going through a network stack.
>
> I see... But that is not good for diskless clusters. Am I right?

No, that isn't correct. Our largest clusters are diskless and use SM. They simply setup a /tmp area in memory to hold the SM region. It preserves the performance, as Jeff said.

> assume processes are on a node (which has no disk). In this case, their communication go though network (from computing node to server) then IO and then network again (from server to computing node).
>
> Regards,
> Mahmood
>
> From: Jeff Squyres <jsquyres_at_[hidden]>
> To: Mahmood Naderan <nt_mahmood_at_[hidden]>; Open MPI Users <users_at_[hidden]>
> Sent: Saturday, October 27, 2012 6:19 PM
> Subject: Re: [OMPI users] openmpi shared memory feature
>
> On Oct 27, 2012, at 10:49 AM, Mahmood Naderan wrote:
>
> > Why openmpi uses shared memory model?
>
> Because communicating through shared memory when sending messages between processes on the same server is far faster than going through a network stack.
>
> > this can be disabled though by setting "--mca ^sm".
> > It seems that by default openmpi uses such feature (shared memory backing files) which is strange.
> >
> > Regards,
> > Mahmood
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
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>
>
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