From: Richard Treumann Date: January 31, 2008 9:23:05 AM CST To: "Mailing list for discussion of MPI 2.1" Subject: Re: [mpi-21] Ballot 4 - MPI_File_set_info update or replacement Reply-To: "Mailing list for discussion of MPI 2.1" I think we have an overall ambiguity about what the "current set of hints" is. This ambiguity is evident in the question about what MPI_FILE_INFO_GET returns and in this discussion too. If an implementation supports 5 file hints then it must select a value for each of these hints an MPI_FILE_OPEN. If there is an MPI_Info that stipulates 2 of the hints then how many hints are in the "current set of hints"? 2 or 5? I would say there are 5 and I think it makes sense for MPI_FILE_GET_INFO to return all 5 (key,value) pairs.( ( Two more specific points -( ( 1) I would expect that if at MPI_FILE_OPEN the implementation is given non-default hints ("A","yes") and ("B","no") and then at MPI_FILE_INFO_SET is given ("B","yes") the net effect is that hint "A" remains as set and hint "B" is altered (if possible). If there is a hint "C" which has never been mentioned it will have received a default value at MPI_FILE_OPEN and the MPI_FILE_INFO_SET which does not mention "C" will leave that default unchanged.( ( Is the "clarification" saying hint "A" must return to default when MPI_FILE_INFO_SET fails to mention it? If that is the intent then I need to be convinced. If we decide this is to be blessed then we probably need to say that any use of MPI_FILE_SET_INFO must first call MPI_FILE_GET_INFO, tweek the INFO it gets back from MPI_FILE_GET_INFO and pass that to MPI_FILE_SET_INFO to avoid unexpected changes to the set of hints that is "in effect".( ( 2) Since a hint is a hint, not a command, it can be rejected. It is possible that some hint can be honored at MPI_FILE_OPEN but once it has been honored, cannot be altered at reasonable cost. ( ( For example, maybe somebody's MPI_FILE_OPEN could accept a hint ("buffer_size", "dynamic-64MB") meaning "start with a 64MB buffer but be prepared to accept changes to buffer size". If the user has set hint ("buffer_size", "64MB") at FILE_OPEN, the implelentation would omit whatever synchs are needed to preserve the ability to change on the fly. Passing ("buffer_size", "dynamic-16MB") to MPI_FILE_SET_INFO could be honored if the user had chosen "dynamic" at FILE_OPEN but would need to be ignored if he had not.( ( For most implementations, a hint like "buffer_size" could not be honored at all after the first file read or write had been done.( ( 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( ( ( mpi-21-bounces@XXXXXXXXXXX wrote on 01/31/2008 08:24:51 AM:( ( > This is a proposal for MPI 2.1, Ballot 4.( > ( > I'm asking especially the implementors to check, whether( > this interpretation is implemented in their MPI implementations,( > or does not contradict to the existing implementation.( > ( > This is a follow up to:( > MPI_File_set_info( > in http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-( > errata/index.html( > with mail discussion not yet existing( > ___________________________________( > ( > Proposal:( > Add in MPI-2.0 Sect. 9.2.8, File Info, page 218, after line 18 the ( > following sentences:( > ( > With MPI_FILE_SET_VIEW and MPI_FILE_SET_INFO the current setting( > of all hints used by the system to this open file is updated by ( > the (key,value) pairs in the info argument.( > ___________________________________( > Rationale for this clarification:( > This text was missing. It was not clear, whether a info handles( > in MPI_FILE_SET_VIEW and MPI_FILE_SET_INFO are updating or replacing( > the current set of used hints. ( > The developers from ROMIO decided to update the current set of used hints.( > Therefore, this behavior should be the expected behavior of a majority( > of users.( > ___________________________________( > ( > Best regards( > Rolf( > ( > ( > ( > ( > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifn _______________________________________________ mpi-21 mailing list mpi-21@XXXXXXXXXXX http://lists.cs.uiuc.edu/mailman/listinfo/mpi-21