Open MPI logo

Open MPI Development Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Development mailing list

From: Gleb Natapov (glebn_at_[hidden])
Date: 2007-05-10 13:02:40


On Thu, May 10, 2007 at 05:56:13PM +0300, Michael S. Tsirkin wrote:
> > Quoting Jeff Squyres <jsquyres_at_[hidden]>:
> > Subject: Re: [ewg] Re: [OMPI devel] Re: OMPI over ofed?udapl -?bugs?opened
> >
> > On May 10, 2007, at 10:28 AM, Michael S. Tsirkin wrote:
> >
> > >>What is the advantage of this approach?
> > >
> > >Current ipoib cm uses this approach to simplify the implementation.
> > >Overhead seems insignificant.
> >
> > I think MPI's requirements are a bit different than IPoIB. See
> > Gleb's response. It is not uncommon for MPI apps to have connections
> > open to many peers simultaneously.
>
> You mean, hundreds of QPs between the same pair of hosts?
> Yes, in this case you might start running out of QPs.

Why is it matters that QPs between the same pair of hosts or not.
QPs are global resource, aren't they?

>
> > Registered memory / internal
> > buffering usage is a Big Deal in the MPI / HPC community.
>
> I don't see the connection with the # of QPs.
> They are very cheap in memory.
>
4K is cheap?

--
			Gleb.