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Subject: Re: [OMPI devel] RFC: make predefined handles extern to pointers
From: Richard Graham (rlgraham_at_[hidden])
Date: 2008-12-17 19:04:53

  Is there any way you can quantify the cost ? This seems reasonable, but
would be nice to get an idea what the performance cost is (and not within a
tight loop where everything stays in cache).


On 12/16/08 10:41 AM, "Terry D. Dontje" <Terry.Dontje_at_[hidden]> wrote:

> WHAT: To make predefined handles extern to pointers instead of an
> address of an extern to a structure.
> WHY: To make OMPI more backwards compatible in regards to changes to
> structures that define predefined handles.
> WHERE: In the trunk. ompi/include/ and places in ompi that
> directly use the predefined handles.
> WHEN: 01/24/2009
> TIMEOUT: 01/10/2009
> ____________________
> The point of this change is to improve the odds that an MPI application
> does not have to recompile when changes are made to the OMPI library.
> In this case specifically the predefined handles that use the structures
> for communicators, groups, ops, datatypes, error handlers, win, file,
> and info.
> An example of the changes for the communicator predefined handles can be
> found in the hg tmp workspace at
> ssh://
> Note, the one downfall that Jeff and I could think of by doing this is
> you potentially add one level of indirection but I believe that will be
> a small overhead and if you use one of the predefined handles
> repetitively (like in a loop) that the address will probably be stored
> in a register once and no additional over should be seen due to this change.
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