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Mpjdev, the low-level MPJ device Aamir Shafi Distributed Systems Group 12 th March, 2004.

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Presentation on theme: "Mpjdev, the low-level MPJ device Aamir Shafi Distributed Systems Group 12 th March, 2004."— Presentation transcript:

1 mpjdev, the low-level MPJ device Aamir Shafi Distributed Systems Group 12 th March, 2004

2 Sequence Introduction History of MPJ Overview of java.nio package mpjdev implementation Introduction Packing/Unpacking at the device level Communication Protocols Eager Send Rendezvous Protocol Quick Start Guide to mpjdev Whats next Trinity: Neo... No one has ever done anything like this. Neo: That's why it's going to work.

3 Introduction Parallel Programming Shared Memory Message Passing MPI PVM Has Java got what it takes to be a parallel programming language ?

4 Message Passing in Java (MPJ) Specification Document mpiJava Uses native MPI

5 Pure java MPI-like libraries mpiJava Uses native MPI Best candidate to be developed to MPJ DSGs project MPJ (http://dsg.port.ac.uk/projects/mpj/) is tightly coupled to this efforthttp://dsg.port.ac.uk/projects/mpj/ JMPI Drawback, based on RMI MPJava Based on java.nio Results encouraging No source-code DOGMA – Dead MPP – Basic library

6 Sequence Introduction History of MPJ Overview of java.nio package mpjdev implementation Introduction Packing/Unpacking at the device level Communication Protocols Eager Send Rendezvous Protocol Quick Start Guide to mpjdev Whats next Oracle: You're cuter than I thought. I can see why she likes you.

7 New I/O overview Buffer classes, Conversion among basic data types Direct and Indirect Buffer Scalable Applications No more one thread per client One thread, many clients Multiplex Synchronous I/O using the selectors SocketChannel – New Abstraction Pipe – One way communication

8 Buffer classes in java.nio TBuffer classes, T being all the basic data types Any basic data type can be copied onto the ByteBuffer, (the basic primitive) Buffer can be, Direct, allocateDirect(int) Indirect, allocate(int)

9 a. ByteBuffer buffer = ByteBuffer.allocate(8); b. buffer.putInt(4); c. buffer.flip();

10 a. ByteBuffer buffer = ByteBuffer.allocate(8); b. ByteBuffer buffer = ByteBuffer.allocateDirect(8);

11 Selector Selector provide, connecting, accepting, reading & writing facilities to the SocketChannel OP_WRITE, OP_READ, OP_ACCEPT, OP_CONNECT Depends on native OS facilities Selection performs differently on Windows and Linux

12 Sequence of events for selectors

13 Taming the NIO circus Taming the NIO circus thread 8&start=0&range=15&hilite=false&q= 8&start=0&range=15&hilite=false&q OutOfMemory Exception 4&message= &message= Selectors taking cent percent CPU J2SE beta solves many problems

14 Sequence Introduction History of MPJ Overview of java.nio package mpjdev implementation Introduction Packing/Unpacking at the device level Communication Protocols Eager Send Rendezvous Protocol Quick Start Guide to mpjdev Whats next Neo: What are you trying to tell me? That I can dodge bullets? Morpheus: No, Neo. I'm trying to tell you that when you're ready, you won't have to.

15 mpjdev – Introduction What is device ? Sockets Similar to ADI in MPICH Meant for library developers (MPJ), not application programmers jGMA can use mpjdev

16 mpjdev – Introduction Single JVM Implementation Processes are threads in the single JVM Native implementation Uses native MPI LAPI Implementation Eager-send Rendezous Buffer packing/unpacking are taken from these implementations

17 mpjev functions Comm methods Void send(Buffer, int dest, int tag) Req isend(Buffer, int dest, int tag) Req irecv(Buffer, int src, int tag) For src, ANY_SRC For tag, ANY_TAG Status recv(Buffer, int dest, int tag) Req methods Status Wait() Status Wait(Req[])

18 mpjdev – Connectivity

19 Communication Protocols – Eager Send Sender Receiver Sel Huge Memory at Receiver

20 Rendezvous Protocol 1 Sender Queue 1 Recv Queue Sender Sel 1 Receiver 1 Sender 1: Sender posts send(), Req stored in Queue Sender 2: Sender sends the control message asking if matching recv is posted ? Sender 3: Sender receives response confirming there is a matching recv Sender 4: Sender sends the actual data Receiver 1: Checks if step 2 has already posted recv, if yes, initiates step 3, else posts a req in Que Receiver 2: Checks if step 1 has posted a recv request, if yes, initiates step 3, else posts a request. NOTE :- STEP 1 & 2 needs synchronization Receiver 3: Writes back to sender that recvr is ready to receive Receiver 4: Receives the data

21 Packing/Unpacking of Buffers write(t[] source, int offset,int length) gather(t[] source, int numEls, int offs, int [] indexes) strGather(t[] source, int srcOff, int rank, int exts, int strs, int [] indexes) read(t[] dest, int dstOff, int numEls) scatter(t[] dest, int numEls, int offs, int [] indexes) strScatter(t[] dest, int dstOff, int rank, int exts, int strs, int [] indexes) Java objects, same concepts

22 Message Format Primary header (Eight bytes), First four bytes –nothing Last four byte --size of message Primary PayLoad, Each primitive data type is written as a section, SECTION_HEADER (8 bytes) First byte – Type of Message, int, float etc Last four bytes – Number of Elements in this section SECTION_DATA The actual data itself Should be multiple of 8 Secondary header (Eight Bytes) First Four bytes –nothing Last Four bytes – Size of Java Object Secondary PayLoad Actual java Object in bytes Can Java object be written as a section in Primary Payload ?

23 Message Format, Single Section int intArray[] = new int[2]; int[0] = 1; int[1] = 2; WriteBuffer wBuffer = new WriteBuffer(24); wBuffer.write(intArray, 0,2); wBuffer.pack(); X X X X Size (24) int T X X X 2(NoEls) int[0] int[1] PRIMARY_HEADERSECTION_HEADER 8 bytes

24 Message Format, Multiple Section int intArray[] = new int[2]; long longArray = new long[2]; int[0] = 1; int[1] = 2; longArray[0] = 1L; longArray[1] = 2L; WriteBuffer wBuffer = new WriteBuffer(48); wBuffer.write(intArray, 0,2); wBuffer.write(longArray, 0,2); wBuffer.pack(); X X X X Size (24) int X X X 2(NoEls) int[0] int[1] L X X X 2 long[0] long[1] PRIMARY_HEADERSECTION_HEADERSECTION_DATA 8 bytes S_HEADERS_DATA 8 bytes16 bytes

25 Control Messages Used in Rendezvous Protocol Format Int – Rank of Destination Int – Rank of Source Int – Message Length Int – Message Tag Should be as small as possible

26 Sequence Introduction History of MPJ Overview of java.nio package mpjdev implementation Introduction Packing/Unpacking at the device level Communication Protocols Eager Send Rendezvous Protocol Quick Start Guide to mpjdev Whats next Morpheus: There is a difference between knowing the path and walking the path.

27 Directory Structure

28 Compiling the source files Dependencies, J2SE1.5.0-beta Apache Ant (1.6.1) If you want to compile from the source, otherwise mpjdev.jar is lying in the mpjdev/lib folder You need to add mpjdev.jar in your CLASSPATH

29 Running Examples - Config Configuration mpjdev/conf/mpjdev.conf Total Number of Processes For each Process Sorry – IP address wont work at present I never had to to write an IP

30 Running examples # cd mpjdev/test # javac -classpath../lib/mpjdev.jar:. BufferTest3.java # java -classpath../lib/mpjdev.jar:. BufferTest3 0 (O is the Rank) Tracking problems java –version, is it 1.5. ? Are you using IP ? me

31 Writing your own programs As an example, Two processes Initialize the device CommImpl.init() Get your ID, CommImpl.id() One process packs & sends data, CommImpl.send(Buffer, int dest, int tag) Other process reads data & unpacks CommImpl.recv(Buffer, int src, int tag) Finalize, CommImpl.finish();

32

33 Sequence Introduction History of MPJ Overview of java.nio package mpjdev implementation Introduction Packing/Unpacking at the device level Communication Protocols Eager Send Rendezvous Protocol Quick Start Guide to mpjdev Whats next Neo: Why do my eyes hurt? Morpheus: You've never used them before.

34 A Few experiments No tests, yet Bottlenecks, Transfer of huge messages seems inefficient Queues, java.util.Vector is not good enough Would like to see how many processes, can selector handle ? Potentially thousands Need bench-marks, keeping in view java issues and bottlenecks, and test them Write our own

35 Future Badly need a runtime Shell scripts starting jobs using ssh or rsh ? MPJ, Group communications I thought, I would have completed the whole MPJ, by now Looking for my PhD project, in the same domain Morpheus: Unfortunately, no one can be told what the Matrix is. You have to see it for yourself.

36 Suggestions ?


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