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How to send C++ STL objects in MPI?

January 24, 2012 at 6:45 am PST

A while ago, Brock Palen tweeted me an MPI question: how does one send Standard Template Library (STL) C++ objects in MPI?

The problem that Brock is asking about is that STL objects tend to be variable size and type.  The whole point of the STL is to create flexible, easy-to-use “containers” of arbitrary types.  For example, STL lists allow you to create an arbitrary length list of a given type.

To cite a concrete example, let’s say that my application has an STL vector object named my_vector that contains a bunch of integers.  What parameters do I pass to MPI_SEND to send this beast?

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Recently Voted into MPI-3

January 23, 2012 at 7:03 am PST

In the January MPI Forum meeting, several proposals passed their 2nd votes, meaning that they are “in” MPI-3.  That being said, MPI-3 is not yet finalized (and won’t be for many more months), so changes can still happen.

  • Creating MPI_COMM_SPLIT_TYPE
  • Making the C++ bindings optional
  • Updating RMA (a.k.a., “one-sided”)
  • Creating a new “MPIT” tools interface

I’ll describe each of these briefly below.

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MPI + VFIO on InsideHPC slidecast

January 18, 2012 at 8:08 am PST

Welcome to 2012!  I’m finally about caught up from the Christmas holidays, last week’s travel to the MPI Forum, etc.  It’s time to finally get my blogging back on.

Let’s start with a short one…

Rich Brueckner from InsideHPC interviewed me right before the Christmas break about the low Ethernet MPI latency demo that I gave at SC’11.  I blogged about this stuff before, but in the slidecast that Rich posted, I provide a bit more detail about how this technology works.

Remember that this is Cisco’s 1st generation virtualized NIC; our 2nd generation is coming “soon,” and will have significantly lower MPI latency (I hate being fuzzy and not quoting the exact numbers, but the product is not yet released, so I can’t comment on it yet.  I’ll post the numbers when the product is actually available).

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MPI_VACATION(2011)

December 30, 2011 at 10:00 am PST
MPI_Bcast("Hi, this is Jeff Squyres.  I'm not in the office this week. "
          "I'll see your message when I return in 2012. Happy New Year!", 
          1, MPI_MESSAGE, MPI_COMM_WORLD);
MPI_Bcast("Beep.", 1, MPI_MESSAGE, MPI_COMM_WORLD);

MPI_RECV(your_message, 1, MPI_MESSAGE, MPI_ANY_RANK, MPI_ANY_TAG, 
         MPI_COMM_WORLD, &status);

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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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