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Linux/kernel/time/test_udelay.c

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  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                 s64 kt1, kt2;
 47                 int time_passed;
 48 
 49                 kt1 = ktime_get_ns();
 50                 udelay(usecs);
 51                 kt2 = ktime_get_ns();
 52                 time_passed = kt2 - kt1;
 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 timespec64 ts;
 91 
 92                 ktime_get_ts64(&ts);
 93                 seq_printf(s, "udelay() test (lpj=%ld kt=%lld.%09ld)\n",
 94                                 loops_per_jiffy, (s64)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");
169 

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