1  /* Benchmark utility functions.
       2     Copyright (C) 2015-2023 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  
      20  static volatile unsigned int dontoptimize = 0;
      21  
      22  void
      23  bench_start (void)
      24  {
      25    /* This loop should cause CPU to switch to maximal frequency.
      26       This makes subsequent measurement more accurate.  We need a side effect
      27       to prevent the loop being deleted by compiler.
      28       This should be enough to cause CPU to speed up and it is simpler than
      29       running loop for constant time.  This is used when user does not have root
      30       access to set a constant frequency.  */
      31  
      32    for (int k = 0; k < START_ITER; k++)
      33      dontoptimize += 23 * dontoptimize + 2;
      34  }