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HOME > Monitoring_and_Data > Oceanic and Atmospheric Data > Reanalysis: Atmospheric Data > wgrib2 -ncpu

wgrib2: -ncpu

The number of threads

Wgrib2 can be compiled to use multiple threads. By default, an OpenMP-enabled version of wgrib2 will use the environement variable OMP_NUM_THREADS. If the environment variable OMP_NUM_THREADS is not defined, the number of threads created is usually the same as the number of cores. The -ncpu option controls the number of threads that will be used by wgrib2. If wgrib2 is not compiled to use OpenMP, this option is quietly ignored. The -ncpu option overrides the OMP_NUM_THREADS environment variable.

When you run an OpenMP-enabled wgrib2 version on a shared system, the performance may be suboptimal. For example, on one of our linux system, we have a 32 cores. The system is shared by many users and during a busy time, there may only be a few cores free at any one time.

The main usage of the -ncpu option is to allocate threads/cpus when you are running multiple copies of wgrib2.


-ncpu N
  N = number of threads


   $ wgrib2 IN.grb -ncpu 3 -new_grid_winds grid -new_grid ncep grid 221 - | wgrib2 - -ncpu 1 -set_grib_type j -ncep_uv OUT.grb

The above line uses 3 threads for regridding and one thread for jpeg2000 compression. The jpeg2000 compression routines can't take advantage of more than one thread. See also:

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Page last modified: May 15, 2005
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