Transcript Java MPI in MATLAB*P

Java MPI in MATLAB*P
Max Goldman
Da Guo
Overview
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Allow nodes to communicate during mm
mode computation
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Implement MPI primitives in Java
Interface to these methods in MATLAB*P
Why Java?
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MATLAB already runs a JVM
Java well suited to network programming
Results
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Basic implementation that works
And some not-so-basic things that work
Performance looks promising
Error handling needs improvement
Some quirks
Basic Architecture
mm mode
Frontend JVM
MATLAB
Node 0
Backend
Node 1
C/C++
JVM
MATLAB
JVM
MATLAB
Node … JVM
MATLAB
Java sockets
Creating the Network
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Problem: each node
needs to know every
other IP address
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One-time
communication
through frontend
Each node opens a
socket to every other
node
10.0.0.1
10.0.0.2
…
10.0.0.1
10.0.0.1
10.0.0.2
…
10.0.0.2
Passing Data
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Java functions operate on double[] buffers
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Pass-by-value across the Java-MATLAB
interface, so methods return buffers
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Conversion is done automagically
In MPI spec, functions take output pointers
Everything comes back as a column!
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Didn’t want to add another wrapper, so users
must use columns or reshape themselves
Making the Call
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mmpi(fname, varargin)
 Function fname can contain MPI calls
 Will be passed directly to mm(…)
 Forces MPI to be separated from *p code
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Eliminates confusion due to e.g. different indexing
Can use mmpi(…) any number of times
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Function does not have to go all the way from
init to fnlz
Making the Call Part II
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Inside mmpi
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First check network, build if needed
Then
pass
control
to mm
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Quirks
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;
MPI Functions (Methods)
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Class MPI
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init and fnlz – “finalize” reserved in Java
Class Comm (MPI.COMM_WORLD)
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send – basic send
recv – basic receive
bcast
use a binary tree algorithm
}
reduce
scatter
gather
scan – uses parallel prefix
Tests
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Calculate the sum of numbers 1--40000
Tests (cont.)
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Find the approximate value of Pi =
Tests (cont.)
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Find maximum value in 40000 random
numbers
Tests (cont.)
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“Scan” example
Demo