From: Purushotham Bangalore Date: January 10, 2008 11:25:15 AM CST To: mpi-21@XXXXXXXXXXXXX Subject: Re: [mpi-21] Proposal EH2: add const keyword to the C bindings Reply-To: mpi-21@XXXXXXXXXXXXX I agree with Dick that there are two different topics that are being discusses on this thread. While the current topic is about adding const keyword, looks like there is sufficient discussion on the send buffer access restriction. In order to assist with the discussion and voting it would be a good idea to have a wiki or something that describes the proposal, pros (benefits), and cons. Specifically I would be interested in listing how the proposed change affects existing programs (both compile time and runtime) from the end-user perspective, how does this impact the implementations, what performance implications should one expect, etc. Is there a wiki for the forum? I am finding it hard to keep up with all the discussion through email (especially when two different issues are discussed in the same thread). It has been a pretty good discussion and would be nice to capture all this at one place. Puri ----- Original Message ----- From: "Richard Treumann" To: mpi-21@XXXXXXXXXXXXX Sent: Thursday, January 10, 2008 7:53:41 AM (GMT-0600) America/Chicago Subject: Re: [mpi-21] Proposal EH2: add const keyword to the C bindings I have mentioned that I think the proposal for removing the send buffer access restriction is worth examining. I have even said I think it likely (not obvious) that the rule should be relaxed. First we should conclude that keeping it has trivial potential for being important to some MPI implementation in comparison the burden it puts on application writers. Performance matters a lot and always will. I thank those who provided examples of situations where relaxed send buffer rules would be helpful. From the start of this discussion I have assumed there would be defensible parallel algorithms that tempt the programmer to violate the rule. I have also assumed there are probably some programmers who violate the rule, either because they do not know about it or because they think they know enough to be sure the rule is irrelevant. I did not have a good estimate of how often the rule is a potential problem but I did see how it could matter. Finally, I think that unless the problems the send buffer rule creates for MPI application writers are real and significant, we should lean toward keeping it. If we let it go to solve hypothetical problems and later develop an architecture that could really exploit the freedom the rule provides to implementors, we will be unable to get the rule back. Dick BTW - I do not see that the decision about the send buffer rule has much connection to "Proposal EH2: add const keyword to the C bindings". In my opinion, the two discussions should be kept apart . I will tackle the "const" issue in a new thread. The send buffer rule seems to have become the dominant topic of this thread. Dick Treumann - MPI Team/TCEM IBM Systems & Technology Group Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363