glibc/sysdeps/x86/dl-tunables.list

# x86 specific tunables.
# Copyright (C) 2017-2021 Free Software Foundation, Inc.
# This file is part of the GNU C Library.

# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.

# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.

# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# <https://www.gnu.org/licenses/>.

glibc {
  cpu {
    hwcaps {
      type: STRING
    }
    x86_ibt {
      type: STRING
    }
    x86_shstk {
      type: STRING
    }
    x86_non_temporal_threshold {
      type: SIZE_T
    }
    x86_rep_movsb_threshold {
      type: SIZE_T
      # Since there is overhead to set up REP MOVSB operation, REP
      # MOVSB isn't faster on short data.  The memcpy micro benchmark
      # in glibc shows that 2KB is the approximate value above which
      # REP MOVSB becomes faster than SSE2 optimization on processors
      # with Enhanced REP MOVSB.  Since larger register size can move
      # more data with a single load and store, the threshold is
      # higher with larger register size.  Micro benchmarks show AVX
      # REP MOVSB becomes faster apprximately at 8KB.  The AVX512
      # threshold is extrapolated to 16KB.  For machines with FSRM the
      # threshold is universally set at 2112 bytes.  Note: Since the
      # REP MOVSB threshold must be greater than 8 times of vector
      # size and the default value is 4096 * (vector size / 16), the
      # default value and the minimum value must be updated at
      # run-time.  NB: Don't set the default value since we can't tell
      # if the tunable value is set by user or not [BZ #27069].
      minval: 1
    }
    x86_rep_stosb_threshold {
      type: SIZE_T
      # Since there is overhead to set up REP STOSB operation, REP STOSB
      # isn't faster on short data.  The memset micro benchmark in glibc
      # shows that 2KB is the approximate value above which REP STOSB
      # becomes faster on processors with Enhanced REP STOSB.  Since the
      # stored value is fixed, larger register size has minimal impact
      # on threshold.
      minval: 1
      default: 2048
    }
    x86_data_cache_size {
      type: SIZE_T
    }
    x86_shared_cache_size {
      type: SIZE_T
    }
  }
}