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Lots coming up for MPI-3.0

December 23, 2011 at 9:49 am PST

The upcoming January 2012 MPI Forum meeting is the last meeting to get new material into the MPI-3.0 specification.

Specifically, there are three steps to getting something into the MPI specification: a formal reading and two separate votes.  Each of these three steps must happen at a separate meeting.  This makes adding new material a long process… but that’s a good thing in terms of a standard.  You want to be sure.  You need a good amount of time of reflection and investigation before you standardize something for the next 10-20 years.

Of course, due to the deadline, we have a giant list of proposals up for a first reading in January (this is not including the 1st and 2nd votes also on the agenda).  Here’s what’s on the docket so far — some are big, new things, while others are small clarifications to existing language: Read More »

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User-level timers for MPI

May 13, 2011 at 9:45 am PST

Fab Tillier (Microsoft MPI) and I recently proposed a set of user-level timers for MPI.  The following slides are an example of what the interface could be:

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Can we count on MPI to handle large datasets?

April 22, 2011 at 2:25 pm PST

(today’s entry is guest-written by Fab Tillier, Microsoft MPI engineer extraordinaire)

When you send data in MPI, you specify how many items of a particular datatype you want to send in your call to an MPI send routine.  Likewise, when you read data from a file, you specify how many datatype elements to read.

This “how many” value is referred to in MPI as a count parameter, and all of MPI’s functions define count parameters as integers: int in C, INTEGER in Fortran.  This definition often limits users to 231 elements (i.e., roughly two billion elements) because int and INTEGER default to 32 bits on many of today’s platforms.

That may sound pretty big, but consider that a 231 byte file is not really that large by today’s standards — especially in HPC, where datasets can sometimes be terabytes in size.  Reading a ~2 gigabyte file can take (far) less than a second.  Read More »

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