Java MPI in MATLAB*P

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Java MPI in MATLABP

• Max Goldman Da Guo

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Overview

• Allow nodes to communicate during mm mode
  computation
• Implement MPI primitives in Java
• Interface to these methods in MATLABP
• Why Java?
• MATLAB already runs a JVM
• Java well suited to network programming

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Results

• Basic implementation that works
• And some not-so-basic things that work
• Performance looks promising
• Error handling needs improvement
• Some quirks

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Basic Architecture
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Creating the Network
10.0.0.1 10.0.0.2

• Problem each node needs to know every other IP
  address
• One-time communication through frontend
• Each node opens a socket to every other node

10.0.0.110.0.0.2
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Passing Data

• Java functions operate on double buffers
• Conversion is done automagically
• Pass-by-value across the Java-MATLAB interface,
  so methods return buffers
• In MPI spec, functions take output pointers
• Everything comes back as a column!
• Didnt want to add another wrapper, so users must
  use columns or reshape themselves

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Making the Call

• mmpi(fname, varargin)
• Function fname can contain MPI calls
• Will be passed directly to mm()
• Forces MPI to be separated from p code
• Eliminates confusion due to e.g. different
  indexing
• Can use mmpi() any number of times
• Function does not have to go all the way from
  init to fnlz

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Making the Call Part II

• Inside mmpi
• First check network, build if needed
• Thenpasscontrolto mm

function result simpletest(arg) import
mpi. MPI.init if MPI.COMM_WORLD.rank 0
data 42 MPI.COMM_WORLD.send(data, 1, 1,
13) result 0 elseif MPI.COMM_WORLD.rank
1 got MPI.COMM_WORLD.recv(1, 0, 13) result
got(1) end MPI.fnlz

• Quirks

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MPI Functions (Methods)

• Class MPI
• init and fnlz finalize reserved in Java
• Class Comm (MPI.COMM_WORLD)
• send basic send
• recv basic receive
• bcast
• reduce
• scatter
• gather
• scan uses parallel prefix

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Tests

• Calculate the sum of numbers 1--40000

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Tests (cont.)

• Find the approximate value of Pi

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Tests (cont.)

• Find maximum value in 40000 random numbers

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Tests (cont.)

• Scan example

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Demo