sysdeps/x86/hp-timing.h

   1 /* High precision, low overhead timing functions.  x86 version.
   2    Copyright (C) 2018-2019 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    <http://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _HP_TIMING_H
  20 #define _HP_TIMING_H    1
  21
  22 #include <isa.h>
  23
  24 #if MINIMUM_ISA == 686 || MINIMUM_ISA == 8664
  25 /* We always assume having the timestamp register.  */
  26 # define HP_TIMING_AVAIL        (1)
  27 # define HP_SMALL_TIMING_AVAIL  (1)
  28
  29 /* We indeed have inlined functions.  */
  30 # define HP_TIMING_INLINE       (1)
  31
  32 /* We use 64bit values for the times.  */
  33 typedef unsigned long long int hp_timing_t;
  34
  35 /* That's quite simple.  Use the `rdtsc' instruction.  Note that the value
  36    might not be 100% accurate since there might be some more instructions
  37    running in this moment.  This could be changed by using a barrier like
  38    'cpuid' right before the `rdtsc' instruciton.  But we are not interested
  39    in accurate clock cycles here so we don't do this.
  40
  41    NB: Use __builtin_ia32_rdtsc directly since including <x86intrin.h>
  42    makes building glibc very slow.  */
  43 # ifdef USE_RDTSCP
  44 /* RDTSCP waits until all previous instructions have executed and all
  45    previous loads are globally visible before reading the counter.
  46    RDTSC doesn't wait until all previous instructions have been executed
  47    before reading the counter.  */
  48 #  define HP_TIMING_NOW(Var) \
  49   (__extension__ ({                             \
  50     unsigned int __aux;                         \
  51     (Var) = __builtin_ia32_rdtscp (&__aux);     \
  52   }))
  53 # else
  54 #  define HP_TIMING_NOW(Var) ((Var) = __builtin_ia32_rdtsc ())
  55 # endif
  56
  57 # include <hp-timing-common.h>
  58 #else
  59 /* NB: Undefine _HP_TIMING_H so that <sysdeps/generic/hp-timing.h> will
  60    be included.  */
  61 # undef _HP_TIMING_H
  62 # include <sysdeps/generic/hp-timing.h>
  63 #endif
  64
  65 #endif /* hp-timing.h */