sysdeps/x86/cpu-tunables.c

   1 /* x86 CPU feature tuning.
   2    This file is part of the GNU C Library.
   3    Copyright (C) 2017-2024 Free Software Foundation, Inc.
   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 #define TUNABLE_NAMESPACE cpu
  20 #include <stdbool.h>
  21 #include <stdint.h>
  22 #include <unistd.h>             /* Get STDOUT_FILENO for _dl_printf.  */
  23 #include <elf/dl-tunables.h>
  24 #include <string.h>
  25 #include <cpu-features.h>
  26 #include <ldsodefs.h>
  27 #include <dl-tunables-parse.h>
  28 #include <dl-symbol-redir-ifunc.h>
  29
  30 #define CHECK_GLIBC_IFUNC_CPU_OFF(f, cpu_features, name, len)           \
  31   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);        \
  32   if (tunable_str_comma_strcmp_cte (&f, #name))                         \
  33     {                                                                   \
  34       CPU_FEATURE_UNSET (cpu_features, name)                            \
  35       break;                                                            \
  36     }
  37
  38 #define CHECK_GLIBC_IFUNC_CPU_BOTH(f, cpu_features, name, len)          \
  39   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);        \
  40   if (tunable_str_comma_strcmp_cte (&f, #name))                         \
  41     {                                                                   \
  42       if (f.disable)                                                    \
  43         CPU_FEATURE_UNSET (cpu_features, name)                          \
  44       else                                                              \
  45         CPU_FEATURE_SET_ACTIVE (cpu_features, name)                     \
  46       break;                                                            \
  47     }
  48
  49 /* Disable a preferred feature NAME.  We don't enable a preferred feature
  50    which isn't available.  */
  51 #define CHECK_GLIBC_IFUNC_PREFERRED_OFF(f, cpu_features, name, len)     \
  52   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);        \
  53   if (tunable_str_comma_strcmp_cte (&f, #name))                         \
  54     {                                                                   \
  55       cpu_features->preferred[index_arch_##name]                        \
  56         &= ~bit_arch_##name;                                            \
  57       break;                                                            \
  58     }
  59
  60 /* Enable/disable a preferred feature NAME.  */
  61 #define CHECK_GLIBC_IFUNC_PREFERRED_BOTH(f, cpu_features, name, len)    \
  62   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);        \
  63   if (tunable_str_comma_strcmp_cte (&f, #name))                         \
  64     {                                                                   \
  65       if (f.disable)                                                    \
  66         cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name; \
  67       else                                                              \
  68         cpu_features->preferred[index_arch_##name] |= bit_arch_##name;  \
  69       break;                                                            \
  70     }
  71
  72 /* Enable/disable a preferred feature NAME.  Enable a preferred feature
  73    only if the feature NEED is usable.  */
  74 #define CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH(f, cpu_features, name,    \
  75                                               need, len)                \
  76   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);        \
  77   if (tunable_str_comma_strcmp_cte (&f, #name))                         \
  78     {                                                                   \
  79       if (f.disable)                                                    \
  80         cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name; \
  81       else if (CPU_FEATURE_USABLE_P (cpu_features, need))               \
  82         cpu_features->preferred[index_arch_##name] |= bit_arch_##name;  \
  83       break;                                                            \
  84     }
  85
  86 attribute_hidden
  87 void
  88 TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
  89 {
  90   /* The current IFUNC selection is based on microbenchmarks in glibc.
  91      It should give the best performance for most workloads.  But other
  92      choices may have better performance for a particular workload or on
  93      the hardware which wasn't available when the selection was made.
  94      The environment variable:
  95
  96      GLIBC_TUNABLES=glibc.cpu.hwcaps=-xxx,yyy,-zzz,....
  97
  98      can be used to enable CPU/ARCH feature yyy, disable CPU/ARCH feature
  99      yyy and zzz, where the feature name is case-sensitive and has to
 100      match the ones in cpu-features.h.  It can be used by glibc developers
 101      to tune for a new processor or override the IFUNC selection to
 102      improve performance for a particular workload.
 103
 104      NOTE: the IFUNC selection may change over time.  Please check all
 105      multiarch implementations when experimenting.  */
 106
 107   struct cpu_features *cpu_features = &GLRO(dl_x86_cpu_features);
 108
 109   struct tunable_str_comma_state_t ts;
 110   tunable_str_comma_init (&ts, valp);
 111
 112   struct tunable_str_comma_t n;
 113   while (tunable_str_comma_next (&ts, &n))
 114     {
 115       switch (n.len)
 116         {
 117         default:
 118           break;
 119         case 3:
 120           if (n.disable)
 121             {
 122               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX, 3);
 123               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, CX8, 3);
 124               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, FMA, 3);
 125               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, HTT, 3);
 126               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, IBT, 3);
 127               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, RTM, 3);
 128             }
 129           break;
 130         case 4:
 131           if (n.disable)
 132             {
 133               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX2, 4);
 134               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, BMI1, 4);
 135               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, BMI2, 4);
 136               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, CMOV, 4);
 137               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, ERMS, 4);
 138               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, FMA4, 4);
 139               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE2, 4);
 140               CHECK_GLIBC_IFUNC_PREFERRED_OFF (n, cpu_features, I586, 4);
 141               CHECK_GLIBC_IFUNC_PREFERRED_OFF (n, cpu_features, I686, 4);
 142             }
 143           break;
 144         case 5:
 145           {
 146             CHECK_GLIBC_IFUNC_CPU_BOTH (n, cpu_features, SHSTK, 5);
 147           }
 148           if (n.disable)
 149             {
 150               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, LZCNT, 5);
 151               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, MOVBE, 5);
 152               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSSE3, 5);
 153               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, XSAVE, 5);
 154             }
 155           break;
 156         case 6:
 157           if (n.disable)
 158             {
 159               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, POPCNT, 6);
 160               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_1, 6);
 161               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_2, 6);
 162               if (memcmp (n.str, "XSAVEC", 6) == 0)
 163                 {
 164                   /* Update xsave_state_size to XSAVE state size.  */
 165                   cpu_features->xsave_state_size
 166                     = cpu_features->xsave_state_full_size;
 167                   CPU_FEATURE_UNSET (cpu_features, XSAVEC);
 168                 }
 169             }
 170           break;
 171         case 7:
 172           if (n.disable)
 173             {
 174               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512F, 7);
 175               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, OSXSAVE, 7);
 176             }
 177           break;
 178         case 8:
 179           if (n.disable)
 180             {
 181               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512CD, 8);
 182               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512BW, 8);
 183               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512DQ, 8);
 184               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512ER, 8);
 185               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512PF, 8);
 186               CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512VL, 8);
 187             }
 188           CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Slow_BSF, 8);
 189           break;
 190         case 11:
 191             {
 192               CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Prefer_ERMS,
 193                                                 11);
 194               CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Prefer_FSRM,
 195                                                 11);
 196               CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH (n, cpu_features,
 197                                                      Slow_SSE4_2,
 198                                                      SSE4_2,
 199                                                      11);
 200             }
 201           break;
 202         case 15:
 203             {
 204               CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
 205                                                 Fast_Rep_String, 15);
 206             }
 207           break;
 208         case 16:
 209             {
 210               CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
 211                 (n, cpu_features, Prefer_No_AVX512, AVX512F, 16);
 212             }
 213           break;
 214         case 18:
 215             {
 216               CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
 217                                                 Fast_Copy_Backward, 18);
 218             }
 219           break;
 220         case 19:
 221             {
 222               CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
 223                                                 Fast_Unaligned_Load, 19);
 224               CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
 225                                                 Fast_Unaligned_Copy, 19);
 226             }
 227           break;
 228         case 20:
 229             {
 230               CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
 231                 (n, cpu_features, Prefer_No_VZEROUPPER, AVX, 20);
 232             }
 233           break;
 234         case 23:
 235             {
 236               CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
 237                 (n, cpu_features, AVX_Fast_Unaligned_Load, AVX, 23);
 238             }
 239           break;
 240         case 24:
 241             {
 242               CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
 243                 (n, cpu_features, MathVec_Prefer_No_AVX512, AVX512F, 24);
 244             }
 245           break;
 246         case 26:
 247             {
 248               CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
 249                 (n, cpu_features, Prefer_PMINUB_for_stringop, SSE2, 26);
 250             }
 251           break;
 252         }
 253     }
 254 }
 255
 256 #if CET_ENABLED
 257 attribute_hidden
 258 void
 259 TUNABLE_CALLBACK (set_x86_ibt) (tunable_val_t *valp)
 260 {
 261   if (tunable_strcmp_cte (valp, "on"))
 262     GL(dl_x86_feature_control).ibt = cet_always_on;
 263   else if (tunable_strcmp_cte (valp, "off"))
 264     GL(dl_x86_feature_control).ibt = cet_always_off;
 265   else if (tunable_strcmp_cte (valp, "permissive"))
 266     GL(dl_x86_feature_control).ibt = cet_permissive;
 267 }
 268
 269 attribute_hidden
 270 void
 271 TUNABLE_CALLBACK (set_x86_shstk) (tunable_val_t *valp)
 272 {
 273   if (tunable_strcmp_cte (valp, "on"))
 274     GL(dl_x86_feature_control).shstk = cet_always_on;
 275   else if (tunable_strcmp_cte (valp, "off"))
 276     GL(dl_x86_feature_control).shstk = cet_always_off;
 277   else if (tunable_strcmp_cte (valp, "permissive"))
 278     GL(dl_x86_feature_control).shstk = cet_permissive;
 279 }
 280 #endif