On Tue, Oct 16, 2012 at 01:35:08PM +0000, Hubert Ritzdorf wrote:

Hi,

I think that there is a problem in the definition of info argument "accumulate_ops" of MPI_Win_create functions (Page 406, Line 4-9 of MPI 3.0 document).

(*) A value is missing if not all concurrent accumulate calls perform the same operation. Possible values might be: "not_same_op" or "false" This would be illegal (as described in the semantics section). The NO_OP was an exception to allow querying a flag with our "fake atomic reads" while performing atomic updates CAS etc.. So really only the two mentioned combinations are legal.

(*) The actual default value of "same_op_no_op" breaks the backward compatibility and causes problems in portability of applications, since a MPI implementation is not required to evaluate (recognize) info keys. Therefore, "not_same_op" must be the default value of info argument "accumulate_ops". Default value means that this is the default semantic if the key is not set (or not evaluated). So a valid user program in MPI-2.2 was only allowed to use the same OP for concurrent accumulates. In MPI-3.0 it may use the same op and also NO_OP in addition. Thus, this richer semantic cannot break backward compatibility. Setting the info key enables the user to enable the more limited MPI-2.2 semantics which may unlock a set of richer optimizations possible in the library.

Best, Torsten -- ### qreharg rug ebs fv crryF ------------- http://www.unixer.de/ ----- Torsten Hoefler | Assistant Professor Dept. of Computer Science | ETH Z�rich Universit�tsstrasse 6 | Zurich-8092, Switzerland CAB E 64.1 | Phone: +41 76 309 79 29