OpenBLAS/docs/runtime_variables.md

OpenBLAS checks the following environment variables on startup:

• OPENBLAS_NUM_THREADS: the number of threads to use (for non-OpenMP builds
  of OpenBLAS)

• OMP_NUM_THREADS: the number of threads to use (for OpenMP builds - note
  that setting this may also affect any other OpenMP code)

• OPENBLAS_DEFAULT_NUM_THREADS: the number of threads to use, irrespective if
  OpenBLAS was built for OpenMP or pthreads

• OPENBLAS_MAIN_FREE=1: this can be used to disable automatic assignment of
  cpu affinity in OpenBLAS builds that have it enabled by default

• OPENBLAS_THREAD_TIMEOUT: this can be used to define the length of time
  that idle threads should wait before exiting

• OMP_ADAPTIVE=1: this can be used in OpenMP builds to actually remove any
  surplus threads when the number of threads is decreased

DYNAMIC_ARCH builds also accept the following:

• OPENBLAS_VERBOSE:

  • set this to 1 to enable a warning when there is no exact match for the
    detected cpu in the library
  • set this to 2 to make OpenBLAS print the name of the cpu target it
    autodetected

• OPENBLAS_CORETYPE: set this to one of the supported target names to
  override autodetection, e.g., OPENBLAS_CORETYPE=HASWELL

• OPENBLAS_L2_SIZE: set this to override the autodetected size of the L2
  cache where it is not reported correctly (in virtual environments)

Deprecated variables still recognized for compatibilty:

• GOTO_NUM_THREADS: equivalent to OPENBLAS_NUM_THREADS
• GOTOBLAS_MAIN_FREE: equivalent to OPENBLAS_MAIN_FREE
• OPENBLAS_BLOCK_FACTOR: this applies a scale factor to the GEMM "P"
  parameter of the block matrix code, see file driver/others/parameter.c