> From: "Rob Latham" <robl@mcs.anl.gov>
>
> On Mon, May 06, 2013 at 02:30:15PM -0500, Bob Cernohous wrote:
> > > From: Rob Ross <rross@mcs.anl.gov>
> > >
> > > Should we consider this as interest in working on this problem on
> > > the IBM side :)? -- Rob
> >
> > Say what?! ;)
>
> RobR's excited that IBM's looking at the ROMIO piece of DCMF.  We
> thought we were on our own with that one.
>
>  
> > I was looking more for agreement that collective i/o is 'what it
> > is'... and maybe some idea if we just have some known limitations on
> > scaling it.  Yes, that BG alltoallv is a bigger problem that we can avoid
> > with an env var -- is that just going to have to be 'good enough'?  (I
> > think that Jeff P wrote that on BG/P and got good performance with that
> > alltoallv.  Trading memory for performance, not unusual, and at least it's
> > selectable.)
>
> I can't test while our Blue Gene is under maintenance.    I know the
> environment variable selection helps only a little bit (like improves
> scaling from 4k to 8k maybe?  don't have the notes offhand).

Ouch.  So you've seen the scaling failures at 8k... ranks? racks?  Kevin is failing at... 16 racks x 16 ranks per node... I think ... so 256k ranks.