1 | /* Benchmark utility functions. |
2 | Copyright (C) 2015-2022 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 | |
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 freqency. |
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 freqency. */ |
31 | |
32 | for (int k = 0; k < START_ITER; k++) |
33 | dontoptimize += 23 * dontoptimize + 2; |
34 | } |
35 | |