[mpi-21] Ballot 4 - MPI_File_set_info update or replacement

Thu Jan 31 13:03:59 CST 2008

Rajeev

I think you just agreed with the interpretation I advocated.  Neither the
proposal or rationale made this at all clear to me.  How about?

Proposal:
Add in MPI-2.0 Sect. 9.2.8, File Info, page 218, after line 18 the
following sentences:

   When an info object that mentions a subset of valid hints
   is passed to MPI_FILE_SET_VIEW or MPI_FILE_SET_INFO, there
   will be no effect on previously set or defaulted hints that
   the info does not mention.

 ___________________________________
 Rationale for this clarification:
   This text was missing. It was not clear, whether an info object
   in MPI_FILE_SET_VIEW and MPI_FILE_SET_INFO was intended to
   replace only the mentioned hints or was intended to substitute
   a complete new set of hints for the prior set.
 ___________________________________

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_at_[hidden] wrote on 01/31/2008 12:29:41 PM:

> The intent is that if the user calls MPI_File_set_info (or
> MPI_File_set_view) twice, the 2nd call will only update (if
> possible) the key-vals passed in the 2nd call; others are
> unmodified. If the 2nd call passes MPI_INFO_NULL, nothing will
> change -- it won't nullify previously passed hints.
>
> Rajeev
>
>
> From: mpi-21-bounces_at_[hidden] [mailto:mpi-21-bounces_at_[hidden]]
> On Behalf Of Richard Treumann
> Sent: Thursday, January 31, 2008 9:23 AM
> To: Mailing list for discussion of MPI 2.1
> Subject: Re: [mpi-21] Ballot 4 - MPI_File_set_info update or replacement

> 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_at_[hidden] 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 rabenseifner_at_[hidden]
> > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
> > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
> > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
> > Nobelstr. 19, D-70550 Stuttgart, Germany . (Office: Allmandring 30)
> > _______________________________________________
> > mpi-21 mailing list
> > mpi-21_at_[hidden]
> > http://lists.cs.uiuc.edu/mailman/listinfo/mpi-21
> _______________________________________________
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