libgomp/doc/openmp-environment-variables/gompspincount.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. index:: Environment Variable, Implementation specific setting
   7
   8 .. _gomp_spincount:
   9
  10 GOMP_SPINCOUNT -- Set the busy-wait spin count
  11 **********************************************
  12
  13 Description:
  14   Determines how long a threads waits actively with consuming CPU power
  15   before waiting passively without consuming CPU power.  The value may be
  16   either ``INFINITE``, ``INFINITY`` to always wait actively or an
  17   integer which gives the number of spins of the busy-wait loop.  The
  18   integer may optionally be followed by the following suffixes acting
  19   as multiplication factors: ``k`` (kilo, thousand), ``M`` (mega,
  20   million), ``G`` (giga, billion), or ``T`` (tera, trillion).
  21   If undefined, 0 is used when :envvar:`OMP_WAIT_POLICY` is ``PASSIVE``,
  22   300,000 is used when :envvar:`OMP_WAIT_POLICY` is undefined and
  23   30 billion is used when :envvar:`OMP_WAIT_POLICY` is ``ACTIVE``.
  24   If there are more OpenMP threads than available CPUs, 1000 and 100
  25   spins are used for :envvar:`OMP_WAIT_POLICY` being ``ACTIVE`` or
  26   undefined, respectively; unless the :envvar:`GOMP_SPINCOUNT` is lower
  27   or :envvar:`OMP_WAIT_POLICY` is ``PASSIVE``.
  28
  29 See also:
  30   :ref:`OMP_WAIT_POLICY`