“Where all the cool kids hang out”. The Big Issue:. Counts Larger Than . 2. 31. Counts are expressed as “. int. ” / “INTEGER”. Usually limited to . 2. 31. Propose a new type: . MPI_Count. ID: 459547 Download Presentation
“Where all the cool kids hang out”. The Big Issue:. Counts Larger Than . 2. 31. Counts are expressed as “. int. ” / “INTEGER”. Usually limited to . 2. 31. Propose a new type: . MPI_Count.
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Presentation on theme: "Backward Compatibility WG"— Presentation transcript:
Slide1
Backward Compatibility WG
“Where all the cool kids hang out”
Slide2
The Big Issue:Counts Larger Than 231
Counts are expressed as “int” / “INTEGER”Usually limited to 231Propose a new type: MPI_CountCan be larger than an int / INTEGER“Mixed sentiments” within the ForumIs it useful? Do we need it? …oy!
MPI_SEND(void *
buf, int count, …)
MPI_SEND(void *
buf
,
MPI_Count
count, …)
Slide3
Do we need MPI_Count?
YES
Some users have asked for itTrivially send large msgs.No need to make a datatypePOSIX went to size_tWhy not MPI?Think about the future:Bigger RAM makes 231 relevantDatasets getting largerDisk IO getting largerCoalescing off-node msgs.
NO
Very few usersAffects many, many MPI API functionsPotential incompatibilitiesE.g., mixing int and MPI_Count in the same application
✔
Slide4
Ok, so how to do it? (1 of 2)
Use MPI_Count only for new MPI-3 routinesChange C bindingsRely on C auto-promotionOnly fix MPI IO functionsWhere MPI_BYTE is usedNew, duplicate functionsE.g., MPI_SEND_LARGE
✖
Inconsistent,
confusing to users
✖
Bad for Fortran, bad
for C OUT params
✖
Inconsistent,
confusing to users
✖
What about sizes,
t
ags, ranks, …
oy
!
Slide5
Ok, so how to do it? (2 of 2)
Fully support large datatypesE.g., MPI_GET_COUNT_LONGCreate a system for API versioningUpdate all functions to use MPI_CountMake new duplicate functions with MPI_Count, MPI_Tag, MPI_Size, …E.g., MPI_SEND_EX
