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Subject: Re: [OMPI devel] RFC: make predefined handles extern to pointers
From: Graham, Richard L. (rlgraham_at_[hidden])
Date: 2008-12-18 08:49:55


No specific test, just an idea how this might impact an app. I am guessing it won't even be noticable.

Rich

----- Original Message -----
From: devel-bounces_at_[hidden] <devel-bounces_at_[hidden]>
To: Open MPI Developers <devel_at_[hidden]>
Sent: Thu Dec 18 07:13:08 2008
Subject: Re: [OMPI devel] RFC: make predefined handles extern to pointers

Richard Graham wrote:
> Terry,
> 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).
>
> Rich
>
>
>
Ok, I guess that would eliminate any of the simple perf tests like IMB,
netperf, and such. So do you have something else in mind, maybe HPCC?

--td
> 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/mpi.h.in 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://www.open-mpi.org/~tdd/hg/predefcompat.
>>
>> 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.
>> _______________________________________________
>> devel mailing list
>> devel_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>>
>
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