From: Patrick Ohly Date: January 10, 2008 4:27:24 AM CST To: mpi-21@XXXXXXXXXXXXX Subject: RE: [mpi-21] Proposal EH2: add const keyword to the C bindings Reply-To: mpi-21@XXXXXXXXXXXXX On Wed, 2008-01-09 at 13:51 -0800, Bronis R. de Supinski wrote: > Not ONCE have I heard that "Restricted access to buffers > of non-blocking MPI send operations was the source of my > problem." Not only do implementations not take advantage > of the opportunity, Probably true, but is hard to verify for all existing implementations. Others have already pointed out that this could change in the future. > the restriction is NOT violated. It is getting violated, sometimes intentionally to avoid extra memory copies in the application when custom communicators would be even worse (Pallas/Intel MPI Benchmarks did it for that reason until very recently), sometimes unintentionally (applying the automated correctness checking of the Intel Cluster Tools to HPCC 1.0.0 found such an instance, see [1]). > This > issue is not worth the time it is being given until someone > can do more than state that it must be causing problems for > "many applications and commercial applications." I see no > reason to sacrifice any potential performance for something > no one slips on. My estimate is that quite a few applications will start to fail as soon as implementations actually use this opportunity. This is not a healthy state for MPI to be in, but it is less obvious what the right solution is. [1] http://www.linuxclustersinstitute.org/conferences/archive/2007/ PDF/ohly_19839.pdf "Automated MPI Correctness Checking: What If There Were a Magic Option?" -- Best Regards Patrick Ohly Senior Software Engineer Intel GmbH Software & Solutions Group Hermuelheimer Strasse 8a Phone: +49-2232-2090-30 50321 Bruehl Fax: +49-2232-2090-29 Germany --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.