PVM

PVM - What Is It? F Stands for: Parallel Virtual Machine F A software tool used to create and execute concurrent or parallel applications. F Operates on a collection of heterogenous Unix computers connected by one or more networks. F Communication accomplished by message passing

PVM - What Is It? F Comprised of two main components –the PVM daemon process (pvmd3) –library interface routines (libpvm3.a, libfpvm3.a & libgpvm3.a) F Public domain software package developed at Oak Ridge National Laboratory.

PVM Components

PVM Daemon (pvmd3) F The PVM daemon (pvmd3) is a Unix process which oversees the operation of user processes within a PVM application and coordinates inter-machine PVM communications.

PVM Daemon (pvmd3) F One daemon runs on each machine configured into your parallel virtual machine. Other users, with their own parallel virtual machines, will have their own pvmd3s running. F User processes communicate with each other through the daemons.

PVM Libraries F libpvm3.a - Library of C language interface routines. Always required. F They contain simple subroutine calls that the application programmer may imbed in concurrent or parallel application code.

Provide ability to: F initiate and terminate processes F pack, send, receive and broadcast messages F synchronize via barriers F query and dynamically change configuration of the parallel virtual machine

Libraries F do not directly communicate to other processes. Instead, they send commands to the local daemon and receive status information back. F Can be installed in user filespace - default is $HOME/pvm3/lib. F Data format conversion (XDR) performed automatically between hosts of different architectures.

Getting Started F Create a directory ~/pvm3/bin/ARCH on each machine for your executable components. F create a soft link to the actual pvm3/lib location (% ln -s ~snell/pvm3/lib ~/pvm3/lib) F PVM_ROOT should be set to ~/pvm3 F Include the appropriate PVM library routine calls in your code.

PVM Routines

Process Control & Information F Processes are identified by process IDs F Each process must acquire a list of all the process IDs in the group F Functions –pvm_mytid –pvm_siblings F Must call pvm_exit() to quit

Sending F Initialize buffers F Pack the message F Send pvm_initsend(PvmDataDefault); pvm_pkint(&token, count, stride); pvm_send(dest, msgtag);

Receiving F Receive the message F Unpack pvm_recv(src, msgtag); pvm_upkint(&token, count, stride);

Compile Your Application Components F Always need libpvm3.a library. F % cc -o myprog myprog.c - I$PVM_ROOT/include - L$PVM_ROOT/lib/$PVM_ARCH -lpvm3 F For Dynamic Groups, also need libgpvm3.a added before libpvm3.a F Make sure that executable components are located in ~/pvm3/bin/ARCH on each machine as required.

Create your PVM hostfile F Your PVM hostfile defines your parallel virtual machine. It contains the names of all desired machines, one per line F Must reside only on the machine where you start up PVM F The filename can be whatever you like F Comment lines start with "#" F Precede hostname with "&" if dynamically added later

Other options permitted: F lo = login userid F pw = password entry required F dx = daemon path if not using default F ep = executable program component paths if not using default ~/pvm3/bin/ARCH

Create Your $HOME/.rhosts file F The.rhosts is a standard Unix "trusted hosts" file - permits remote login and command execution without password. It is not unique to PVM - simply used by PVM. F Must be in your home directory F Should be readable by user only! F Format: host.domain.name userid

Start the Master PVM Daemon F Start up the master (first) daemon. F % pvmd3 hostfile & F Must be started on your local machine F Automatically starts up daemons on all other machines (remote) specified in your hostfile.

Tips F Do not run in the background if using the password (pw) specification in your hostfile. F Should only have one pvmd3 running on each machine in your virtual machine! F PVM console can be started after pvmd3 by typing "pvm". PVM console commands can then be issued.

Execute your application F Begin execution of your program on your local machine F % myprog F What happens from here depends upon your application.

Quit PVM F Make sure all application components include a PVM library call of "pvmfexit(info)" or "pvm_exit()". F Halting the master pvmd3 will automatically kill all other pvmd3s and all processes enrolled in this PVM. F Running in pvm console mode: use "halt" command

If it won't die F Abnormal terminations of PVM may leave files in /tmp which prevent you from restarting (known bug). Should delete all /tmp/pvm*. files on all machines before restarting the master pvmd3. F Try "~clement/bin/kill-pvms" if all else fails

Miscellaneous & Hints F The most common problem in starting PVM daemons is probably due to daemons already running on the machine(s), or the existence of a /tmp/pvmd.uid file. You'll need to kill old daemons and/or remove any /tmp/pvmd.uid files. F The second most common problem is probably due to incorrect.rhost files.

Other Problems F Another, less frequent startup problem is due to.cshrc files that require interactive input or which display messages.

Be Careful F Be careful of concurrent I/O to the same files in a shared filesystem! For concurrent I/O (writing) in a shared filesystem, you may want to implement a scheme to assign unique names to output files.

Your Assignment F Specifications are on the web F Using a Jacobi 5 point stencil, solve the 2D steady state temperature distribution problem on a 768 x 768 grid. F Use formula 2.1 on page 34 F Report your execution times on 2, 4, and 8 processors.