Parallel processing

You can enable or disable parallel processing at link time or at runtime. A program does not use parallelism in VECLIB unless parallel processing is enabled at both link time and at runtime.

Linking for parallel or non parallel processing

To enable parallel processing at link time, your link step must produce a multithreaded executable. On HP-UX systems, use the +O3 and +Oparallel compiler options to get a multithreaded executable when you link with the HP Fortran compiler; use +O3 and +Oopenmp when you link with the HP C compiler; and use +Oopenmp when you link with the HP aC++ compiler:

f90 [options including +O3 +Oparallel] file ... –Wl,–aarchive_shared −lveclib

cc[options including +O3 +Oopenmp] file ... –Wl,–aarchive_shared −lveclib −lcl −lm

aCC [options including +Oopenmp] file ... –Wl,–aarchive_shared −lveclib −lcl −lm

To disable VECLIB’s automatic parallelism at link time, omit the +Oparallel and +Oopenmp options:

f90 [options] file ... –Wl,–aarchive_shared −lveclib

cc[options] file ... –Wl,–aarchive_shared −lveclib −lcl −lm aCC [options] file ... –Wl,–aarchive_shared −lveclib −lcl −lm

VECLIB for Linux is always multithreaded enabled.

Controlling VECLIB parallelism at runtime

When you enable parallelism at link time, three methods are available at runtime to specify the extent of parallel processing in MLIB.

•Use MLIB_NUMBER_OF_THREADS, a shell environment variable that allows you to enable parallelism within MLIB subprograms and to specify the maximum number of threads that can be used in parallel regions.

Not setting MLIB_NUMBER_OF_THREADS has the same result as setting it to 1; that is, parallel processing is disabled within MLIB subroutines. Setting MLIB_NUMBER_OF_THREADS to the number of CPUs in the system, or greater, allows parallelized MLIB subprograms to use as many CPUs as are available to the process.

The following command lines show the C shell syntax and Korn shell syntax to use when setting the variable to eight processors:

For C shell:

setenv MLIB_NUMBER_OF_THREADS 8

18HP MLIB User’s Guide