[mpich-devel] ROMIO collective i/o memory use

[Rob Latham]

On Mon, May 06, 2013 at 02:30:15PM -0500, Bob Cernohous wrote:
> > From: Rob Ross <rross at 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). 

==rob

-- 
Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA