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

Bob Cernohous bobc at us.ibm.com
Mon May 6 14:30:15 CDT 2013

> 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?! ;)

Meaning we can get rid of all o(p) allocations?  Not sure how you do 
internal collectives on behalf of the app/mpi-io without at least some of 
those.  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 
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