PAR Technologies V5 manual Controlling ParaStation5 communication paths

ParaStation5 TCP bypass

In order to run applications linked with one of those MPI libraries, ParaStation5 provides dedicated mpirun commands. The processes for those type of parallel tasks are spawned obeying all restrictions described in Section 5.3, “Controlling process placement”. Of course, the data transfer will be based on the communication channels supported by the particular MPI library. For MPIch using ch_p4 (TCP), ParaStation5 provides an alternative, see Section 5.7, “ParaStation5 TCP bypass”.

The command mpirun-ipath-psrunning programs linked with InfiniPath™ MPI is part of the psipath package. For details how to obtain this package, please contact <support@par-tec.com>.

For more information refer to mpirun_chp4(8), mpirun_chgm(8), mpirun-ipath-ps(8), mpirun_openib(8) and mpirun_elan(8).

Using the ParaStation5 command mpiexec, any parallel application supporting the PMI protocol, which is part of the MPI2 standard, may be run using the ParaStation process environment. Therefore, many other MPI2 compatible MPI libraries are now supported by ParaStation5.

It is also possible to run serial applications, thus applications not parallelized with MPI, within ParaStation. ParaStation distinguishes between serial tasks allocating a dedicated CPU within the resource management system and administrative tasks not allocating a CPU. To execute a serial program, run mpiexec -n 1 To run an administrative task, use pssh or mpiexec -A-n 1.

For more details on how to start-up serial and parallel jobs refer to mpiexec(8), pssh(8) and the ParaStation5 User's Guide.

5.7.ParaStation5 TCP bypass

ParaStation5 offers a feature called "TCP bypass", enabling applications based on TCP to use the efficient p4sock protocol. The data will be redirected within the kernel to the p4sock protocol. No modifications to the application are necessary!

To automatically configure the TCP bypass during ParaStation startup, insert a line like

Env PS_TCP FirstAddress-LastAddress

in the p4sock-section of the configuration file parastation.conf, were FirstAddress and LastAddress are the first and last IP addresses for which the bypass should be configured.

To enable the bypass for a pair of processes, the library libp4tcp.so, located in the directory /opt/ parastation/lib64 must be pre-loaded by both processes using:

export LD_PRELOAD=/opt/parastation/lib64/libp4tcp.so

For parallel and serial tasks launched by ParaStation, this environment variable is exported to all processes by default. Please refer to ps_environment(5).

It's not recommended to insertlibp4tcp.so in the global preload configuration file /etc/ld.so.preload, as this may hang connections to daemon processes started up before the bypass was configured.

See also p4tcp(8).

5.8. Controlling ParaStation5 communication paths

ParaStation uses different communication paths, see Section 5.1, “ParaStation5 pscom communication library” for details. In order to restrict the paths to use, a number of environment variables are recognized by ParaStation.

ParaStation5 Administrator's Guide 21