sysdeps/x86/dl-tunables.list

   1 # x86 specific tunables.
   2 # Copyright (C) 2017-2022 Free Software Foundation, Inc.
   3 # This file is part of the GNU C Library.
   4
   5 # The GNU C Library is free software; you can redistribute it and/or
   6 # modify it under the terms of the GNU Lesser General Public
   7 # License as published by the Free Software Foundation; either
   8 # version 2.1 of the License, or (at your option) any later version.
   9
  10 # The GNU C Library is distributed in the hope that it will be useful,
  11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 # Lesser General Public License for more details.
  14
  15 # You should have received a copy of the GNU Lesser General Public
  16 # License along with the GNU C Library; if not, see
  17 # <https://www.gnu.org/licenses/>.
  18
  19 glibc {
  20   cpu {
  21     hwcaps {
  22       type: STRING
  23     }
  24     x86_ibt {
  25       type: STRING
  26     }
  27     x86_shstk {
  28       type: STRING
  29     }
  30     x86_non_temporal_threshold {
  31       type: SIZE_T
  32     }
  33     x86_rep_movsb_threshold {
  34       type: SIZE_T
  35       # Since there is overhead to set up REP MOVSB operation, REP
  36       # MOVSB isn't faster on short data.  The memcpy micro benchmark
  37       # in glibc shows that 2KB is the approximate value above which
  38       # REP MOVSB becomes faster than SSE2 optimization on processors
  39       # with Enhanced REP MOVSB.  Since larger register size can move
  40       # more data with a single load and store, the threshold is
  41       # higher with larger register size.  Micro benchmarks show AVX
  42       # REP MOVSB becomes faster apprximately at 8KB.  The AVX512
  43       # threshold is extrapolated to 16KB.  For machines with FSRM the
  44       # threshold is universally set at 2112 bytes.  Note: Since the
  45       # REP MOVSB threshold must be greater than 8 times of vector
  46       # size and the default value is 4096 * (vector size / 16), the
  47       # default value and the minimum value must be updated at
  48       # run-time.  NB: Don't set the default value since we can't tell
  49       # if the tunable value is set by user or not [BZ #27069].
  50       minval: 1
  51     }
  52     x86_rep_stosb_threshold {
  53       type: SIZE_T
  54       # Since there is overhead to set up REP STOSB operation, REP STOSB
  55       # isn't faster on short data.  The memset micro benchmark in glibc
  56       # shows that 2KB is the approximate value above which REP STOSB
  57       # becomes faster on processors with Enhanced REP STOSB.  Since the
  58       # stored value is fixed, larger register size has minimal impact
  59       # on threshold.
  60       minval: 1
  61       default: 2048
  62     }
  63     x86_data_cache_size {
  64       type: SIZE_T
  65     }
  66     x86_shared_cache_size {
  67       type: SIZE_T
  68     }
  69   }
  70 }