Commit e704f93a authored by David Riley's avatar David Riley Committed by John Stultz

kernel: time: Add udelay_test module to validate udelay

Create a module that allows udelay() to be executed to ensure that
it is delaying at least as long as requested (with a little bit of
error allowed).

There are some configurations which don't have reliably udelay
due to using a loop delay with cpufreq changes which should use
a counter time based delay instead.  This test aims to identify
those configurations where timing is unreliable.
Signed-off-by: default avatarDavid Riley <davidriley@chromium.org>
Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
parent 1af447bd
......@@ -13,6 +13,7 @@ obj-$(CONFIG_TICK_ONESHOT) += tick-oneshot.o
obj-$(CONFIG_TICK_ONESHOT) += tick-sched.o
obj-$(CONFIG_TIMER_STATS) += timer_stats.o
obj-$(CONFIG_DEBUG_FS) += timekeeping_debug.o
obj-$(CONFIG_TEST_UDELAY) += udelay_test.o
$(obj)/time.o: $(obj)/timeconst.h
......@@ -29,3 +30,4 @@ quiet_cmd_bc = BC $@
targets += timeconst.h
$(obj)/timeconst.h: $(obj)/hz.bc $(src)/timeconst.bc FORCE
$(call if_changed,bc)
/*
* udelay() test kernel module
*
* Test is executed by writing and reading to /sys/kernel/debug/udelay_test
* Tests are configured by writing: USECS ITERATIONS
* Tests are executed by reading from the same file.
* Specifying usecs of 0 or negative values will run multiples tests.
*
* Copyright (C) 2014 Google, Inc.
*
* This software is licensed under the terms of the GNU General Public
* License version 2, as published by the Free Software Foundation, and
* may be copied, distributed, and modified under those terms.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <linux/debugfs.h>
#include <linux/delay.h>
#include <linux/ktime.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#define DEFAULT_ITERATIONS 100
#define DEBUGFS_FILENAME "udelay_test"
static DEFINE_MUTEX(udelay_test_lock);
static struct dentry *udelay_test_debugfs_file;
static int udelay_test_usecs;
static int udelay_test_iterations = DEFAULT_ITERATIONS;
static int udelay_test_single(struct seq_file *s, int usecs, uint32_t iters)
{
int min = 0, max = 0, fail_count = 0;
uint64_t sum = 0;
uint64_t avg;
int i;
/* Allow udelay to be up to 0.5% fast */
int allowed_error_ns = usecs * 5;
for (i = 0; i < iters; ++i) {
struct timespec ts1, ts2;
int time_passed;
ktime_get_ts(&ts1);
udelay(usecs);
ktime_get_ts(&ts2);
time_passed = timespec_to_ns(&ts2) - timespec_to_ns(&ts1);
if (i == 0 || time_passed < min)
min = time_passed;
if (i == 0 || time_passed > max)
max = time_passed;
if ((time_passed + allowed_error_ns) / 1000 < usecs)
++fail_count;
WARN_ON(time_passed < 0);
sum += time_passed;
}
avg = sum;
do_div(avg, iters);
seq_printf(s, "%d usecs x %d: exp=%d allowed=%d min=%d avg=%lld max=%d",
usecs, iters, usecs * 1000,
(usecs * 1000) - allowed_error_ns, min, avg, max);
if (fail_count)
seq_printf(s, " FAIL=%d", fail_count);
seq_puts(s, "\n");
return 0;
}
static int udelay_test_show(struct seq_file *s, void *v)
{
int usecs;
int iters;
int ret = 0;
mutex_lock(&udelay_test_lock);
usecs = udelay_test_usecs;
iters = udelay_test_iterations;
mutex_unlock(&udelay_test_lock);
if (usecs > 0 && iters > 0) {
return udelay_test_single(s, usecs, iters);
} else if (usecs == 0) {
struct timespec ts;
ktime_get_ts(&ts);
seq_printf(s, "udelay() test (lpj=%ld kt=%ld.%09ld)\n",
loops_per_jiffy, ts.tv_sec, ts.tv_nsec);
seq_puts(s, "usage:\n");
seq_puts(s, "echo USECS [ITERS] > " DEBUGFS_FILENAME "\n");
seq_puts(s, "cat " DEBUGFS_FILENAME "\n");
}
return ret;
}
static int udelay_test_open(struct inode *inode, struct file *file)
{
return single_open(file, udelay_test_show, inode->i_private);
}
static ssize_t udelay_test_write(struct file *file, const char __user *buf,
size_t count, loff_t *pos)
{
char lbuf[32];
int ret;
int usecs;
int iters;
if (count >= sizeof(lbuf))
return -EINVAL;
if (copy_from_user(lbuf, buf, count))
return -EFAULT;
lbuf[count] = '\0';
ret = sscanf(lbuf, "%d %d", &usecs, &iters);
if (ret < 1)
return -EINVAL;
else if (ret < 2)
iters = DEFAULT_ITERATIONS;
mutex_lock(&udelay_test_lock);
udelay_test_usecs = usecs;
udelay_test_iterations = iters;
mutex_unlock(&udelay_test_lock);
return count;
}
static const struct file_operations udelay_test_debugfs_ops = {
.owner = THIS_MODULE,
.open = udelay_test_open,
.read = seq_read,
.write = udelay_test_write,
.llseek = seq_lseek,
.release = single_release,
};
static int __init udelay_test_init(void)
{
mutex_lock(&udelay_test_lock);
udelay_test_debugfs_file = debugfs_create_file(DEBUGFS_FILENAME,
S_IRUSR, NULL, NULL, &udelay_test_debugfs_ops);
mutex_unlock(&udelay_test_lock);
return 0;
}
module_init(udelay_test_init);
static void __exit udelay_test_exit(void)
{
mutex_lock(&udelay_test_lock);
debugfs_remove(udelay_test_debugfs_file);
mutex_unlock(&udelay_test_lock);
}
module_exit(udelay_test_exit);
MODULE_AUTHOR("David Riley <davidriley@chromium.org>");
MODULE_LICENSE("GPL");
......@@ -1649,6 +1649,15 @@ config TEST_BPF
If unsure, say N.
config TEST_UDELAY
tristate "udelay test driver"
default n
help
This builds the "udelay_test" module that helps to make sure
that udelay() is working properly.
If unsure, say N.
source "samples/Kconfig"
source "lib/Kconfig.kgdb"
......
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