kernel/time/test_udelay.c

   1 /*
   2  * udelay() test kernel module
   3  *
   4  * Test is executed by writing and reading to /sys/kernel/debug/udelay_test
   5  * Tests are configured by writing: USECS ITERATIONS
   6  * Tests are executed by reading from the same file.
   7  * Specifying usecs of 0 or negative values will run multiples tests.
   8  *
   9  * Copyright (C) 2014 Google, Inc.
  10  *
  11  * This software is licensed under the terms of the GNU General Public
  12  * License version 2, as published by the Free Software Foundation, and
  13  * may be copied, distributed, and modified under those terms.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  */
  20
  21 #include <linux/debugfs.h>
  22 #include <linux/delay.h>
  23 #include <linux/ktime.h>
  24 #include <linux/module.h>
  25 #include <linux/uaccess.h>
  26
  27 #define DEFAULT_ITERATIONS 100
  28
  29 #define DEBUGFS_FILENAME "udelay_test"
  30
  31 static DEFINE_MUTEX(udelay_test_lock);
  32 static struct dentry *udelay_test_debugfs_file;
  33 static int udelay_test_usecs;
  34 static int udelay_test_iterations = DEFAULT_ITERATIONS;
  35
  36 static int udelay_test_single(struct seq_file *s, int usecs, uint32_t iters)
  37 {
  38         int min = 0, max = 0, fail_count = 0;
  39         uint64_t sum = 0;
  40         uint64_t avg;
  41         int i;
  42         /* Allow udelay to be up to 0.5% fast */
  43         int allowed_error_ns = usecs * 5;
  44
  45         for (i = 0; i < iters; ++i) {
  46                 struct timespec ts1, ts2;
  47                 int time_passed;
  48
  49                 ktime_get_ts(&ts1);
  50                 udelay(usecs);
  51                 ktime_get_ts(&ts2);
  52                 time_passed = timespec_to_ns(&ts2) - timespec_to_ns(&ts1);
  53
  54                 if (i == 0 || time_passed < min)
  55                         min = time_passed;
  56                 if (i == 0 || time_passed > max)
  57                         max = time_passed;
  58                 if ((time_passed + allowed_error_ns) / 1000 < usecs)
  59                         ++fail_count;
  60                 WARN_ON(time_passed < 0);
  61                 sum += time_passed;
  62         }
  63
  64         avg = sum;
  65         do_div(avg, iters);
  66         seq_printf(s, "%d usecs x %d: exp=%d allowed=%d min=%d avg=%lld max=%d",
  67                         usecs, iters, usecs * 1000,
  68                         (usecs * 1000) - allowed_error_ns, min, avg, max);
  69         if (fail_count)
  70                 seq_printf(s, " FAIL=%d", fail_count);
  71         seq_puts(s, "\n");
  72
  73         return 0;
  74 }
  75
  76 static int udelay_test_show(struct seq_file *s, void *v)
  77 {
  78         int usecs;
  79         int iters;
  80         int ret = 0;
  81
  82         mutex_lock(&udelay_test_lock);
  83         usecs = udelay_test_usecs;
  84         iters = udelay_test_iterations;
  85         mutex_unlock(&udelay_test_lock);
  86
  87         if (usecs > 0 && iters > 0) {
  88                 return udelay_test_single(s, usecs, iters);
  89         } else if (usecs == 0) {
  90                 struct timespec ts;
  91
  92                 ktime_get_ts(&ts);
  93                 seq_printf(s, "udelay() test (lpj=%ld kt=%ld.%09ld)\n",
  94                                 loops_per_jiffy, ts.tv_sec, ts.tv_nsec);
  95                 seq_puts(s, "usage:\n");
  96                 seq_puts(s, "echo USECS [ITERS] > " DEBUGFS_FILENAME "\n");
  97                 seq_puts(s, "cat " DEBUGFS_FILENAME "\n");
  98         }
  99
 100         return ret;
 101 }
 102
 103 static int udelay_test_open(struct inode *inode, struct file *file)
 104 {
 105         return single_open(file, udelay_test_show, inode->i_private);
 106 }
 107
 108 static ssize_t udelay_test_write(struct file *file, const char __user *buf,
 109                 size_t count, loff_t *pos)
 110 {
 111         char lbuf[32];
 112         int ret;
 113         int usecs;
 114         int iters;
 115
 116         if (count >= sizeof(lbuf))
 117                 return -EINVAL;
 118
 119         if (copy_from_user(lbuf, buf, count))
 120                 return -EFAULT;
 121         lbuf[count] = '\0';
 122
 123         ret = sscanf(lbuf, "%d %d", &usecs, &iters);
 124         if (ret < 1)
 125                 return -EINVAL;
 126         else if (ret < 2)
 127                 iters = DEFAULT_ITERATIONS;
 128
 129         mutex_lock(&udelay_test_lock);
 130         udelay_test_usecs = usecs;
 131         udelay_test_iterations = iters;
 132         mutex_unlock(&udelay_test_lock);
 133
 134         return count;
 135 }
 136
 137 static const struct file_operations udelay_test_debugfs_ops = {
 138         .owner = THIS_MODULE,
 139         .open = udelay_test_open,
 140         .read = seq_read,
 141         .write = udelay_test_write,
 142         .llseek = seq_lseek,
 143         .release = single_release,
 144 };
 145
 146 static int __init udelay_test_init(void)
 147 {
 148         mutex_lock(&udelay_test_lock);
 149         udelay_test_debugfs_file = debugfs_create_file(DEBUGFS_FILENAME,
 150                         S_IRUSR, NULL, NULL, &udelay_test_debugfs_ops);
 151         mutex_unlock(&udelay_test_lock);
 152
 153         return 0;
 154 }
 155
 156 module_init(udelay_test_init);
 157
 158 static void __exit udelay_test_exit(void)
 159 {
 160         mutex_lock(&udelay_test_lock);
 161         debugfs_remove(udelay_test_debugfs_file);
 162         mutex_unlock(&udelay_test_lock);
 163 }
 164
 165 module_exit(udelay_test_exit);
 166
 167 MODULE_AUTHOR("David Riley <davidriley@chromium.org>");
 168 MODULE_LICENSE("GPL");