Hp XC System 2.x Software Manuel d'utilisateur télécharger pdf (Page 54)

utilities/libHYPRE_utilities.a:

$(PREFIX) $(MAKE) $(MAKE_J) -C utilities

The modified Makefile is invoked as follows:

$ make PREFIX=’srun -n1 -N1’ MAKE_J=’-j4’

3.9.2 Local Disks on Compute Nodes

The use of a local disk for private, temporary storage may be configured on the compute

nodes of your HP XC system. Contact your system administrator to find out about the local

disks configured on your system.

A local disk is a temporary storage space and does not ho ld data across execution of

applications. Therefore, any information generated by the application during its execution is not

saved o n the local disk once the application has com pleted.

3.9.3 I/O Performance Considerations

Before building and running y our parallel application, I/O performance issues on the HP XC

cluster must be considered.

The I/O co ntrol system provides two basic t ypes of standard file system views to the application:

•Shared

•Private

3.9.3.1 Shared File View

Although a file opened by multiple processes of an application is shared, each processor

maintains a private file pointe r and file position. This means that if a certain order of input or

output f rom multiple pr ocessors is desired, the ap pli cation must synchronize its I/O requests or

position its file pointer such that it acts on t he desired file location.

Output req uests to standard output and standard error are line-buffered, which can be sufficient

output ordering in many cases. A sim ilar effect for other files can be achieved by using append

mode when opening the file with the fopen system call:

fp = fopen ("myfile", "a+");

3.9.3.2 Private File View

Although the shared file approach improves ease of use for most applications, some applications,

especially those written for shared-no thi ng clu st ers, can requir e the use of file s ystems private to

each node. To accommodate these applications, the system must be configured w ith local disk.

For example, assume /tmp and /tmp1 have been configured on each compute node.

Now each process can open up a file named /tmp/myscratch or /tmp1/myother-

scratch and each would see a unique file pointer. If these file system s do not exist local to

the node, an error results.

It is a good idea to use th is option for temporary storage only, and make sure that th e application

deletes the file at th e e nd.

Cexample:fd = open ("/tmp/myscratch", flags)

Fortran example: open (unit=9, file="/tmp1/myotherscratch" )

3-14 Deve loping Applications

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Hp XC System 2.x Software Manuel d'utilisateur Page 54