* OMII, Southampton

Pluggable Architecture for Java HPC Messaging

Mark Baker, Bryan Carpenter*, Aamir ShafiDistributed Systems GroupUniversity of Portsmouth

http://dsg.port.ac.uk

April 22, 2023 2

Presentation Outline• Introduction,• Design and Implementation of MPJ,• Preliminary Performance Evaluation,• Conclusion.

April 22, 2023 3

Introduction • MPI was introduced in June 1994 as a standard message passing API for parallel scientific computing:

–Language bindings for C, C++, and Fortran,• ‘Java Grande Message Passing Workgroup’ defined Java bindings in 98,

• Previous efforts follow two approaches: –Pure Java approach:

• Remote Method Invocation (RMI),• Sockets,

–JNI approach.

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Pure Java Approach• RMI:

–Meant for client server applications, • Java Sockets:

–Java New I/O package:• Adds non-blocking I/O to the Java language, • Direct Buffers:

– Allocated in the native OS memory and the JVM attempts to provide faster I/O,

• Communication performance:• Comparison of Java NIO and C Netpipe (a Ping-Pong

benchmark) drivers,• Java performance similar to C on Fast Ethernet:

– A naïve comparison.– Latency:

» ~125 microseconds,– Throughput:

» ~90 Mbps.

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JNI Approach• Importance of JNI cannot be ignored:

–Where Java fails, JNI makes it work,• Advances in HPC communication hardware have continued:

–Network latency has been reduced to a couple of microseconds,

• ‘Pure Java’ is not a universal solution:–In the presence of Myrinet, no application user

would opt for Fast Ethernet,• Cons:

–Not in spirit of Java philosophy ‘write once, run anywhere’.

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The Problem• For Java messaging:

–There is no ‘one size fits all’ approach,

• Portability and high performance are often contradictory requirements:

–Portability: Pure Java,–High Performance: JNI,

• The choice between portability and high performance should best be left to application users,

• The challenging issue is how to manage these contradictory requirements:

–How to provide a flexible mechanism to help applications swap communication protocols?

April 22, 2023 7

Presentation Outline• Introduction• Design and Implementation• Preliminary Performance Evaluation • Conclusion

April 22, 2023 8

Design• Aims:

–Support swapping various communication devices,

• Two device levels: –The MPJ Device level (mpjdev):

• Separates native MPI-2 device from all other devices,• ‘native MPI-2’ device is a special case:

– Possible to cut through and make use of native implementation of advanced MPI features,

–The xdev Device level (xdev):• ‘gmdev’ – xdev based on GM 2.x comms library,• ‘niodev’ – xdev based on Java NIO API,• ‘smpdev’ – xdev based on Threads API.

April 22, 2023 9

Design

MPJ point to point communications (Base level)

mpjdev (MPJ Device level)

MPJ collective Communications (High level)

Hardware (NIC, Memory etc)

MPJ API

JNI Java NIO

Java Virtual Machine (JVM)

JNI

Native MPIgmdev

ThreadsAPI

smpdev

xdev

niodev

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Implementation• MPJ complies with functionality of MPI-1.2:

–Point to point communications,–Collective communications,–Groups, communicators, and contexts, –Derived datatypes:

• Buffering API,

• Runtime infrastructure:–Allows bootstrapping MPJ processes, –MPJ Daemon could be installed as services,

• Communication protocols: –Java NIO device, –GM 2.x.x device (Myrinet), –Shared memory device (using Threads API), –Native MPI-2 device.

April 22, 2023 11

Presentation Outline• Introduction• Design and Implementation• Preliminary Performance Evaluation• Conclusion

April 22, 2023 12

Preliminary Performance Evaluation • Point-to-point (connected by Fast Ethernet):

–mpiJava 1.2.5 (using MPICH 1.2.5),–MPJ (using Java NIO),–MPICH (1.2.5) (using ch_p4),–LAM/MPI (7.0.9) (using TCP RPI),

• Transfer time and throughput graphs,• Analysis.

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Transfer Time Comparison

MPJ: ~250 microseconds (latency)

mpiJava, LAM/MPI, MPICH: ~125 microseconds (latency)

April 22, 2023 14

Throughput Comparison

MPJ: ~81 MbpsmpiJava: ~84 MbpsLAM/MPI: ~90 MbpsMPICH: ~88 Mbps

April 22, 2023 15

Analysis• General behaviour is similar to other MPI implementations,

• Optimisation areas: –Latency for small messages:

• Currently control message and data is written in two separate SocketChannel write operations,

–Large messages: • Maintaining pool of buffers,

• Understand the anamoly at 16M datapoint.

April 22, 2023 16

Presentation Outline• Introduction• Design and Implementation• Preliminary Performance Evaluation• Conclusion

April 22, 2023 17

Summary• The key issue for Java messaging is not debating pure Java or JNI approach:

–But, providing a flexible mechanism to swap various comm protocols,

• MPJ has a pluggable architecture: –We are implementing ‘niodev’, ‘gmdev’,

‘smpdev’, and native MPI-2 device,• MPJ runtime infrastructure allows bootstrapping MPI processes across various platforms.

April 22, 2023 18

Conclusions• MPJ is the second generation ‘MPI for Java’• Current Status:

–Unit testing, –Optimization,

• Initial version of MPJ follows the same API as mpiJava (and is intended to supersede mpiJava):

–The parallel applications built on top of mpiJava will work with MPJ,

–There are some minor omissions:• Bsend, and explicit packing/unpacking -- see release docs

for more details,

• Arguably, the first “full” MPI library for Java providing a pure Java implementation.

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Questions