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: David Riley <davidri...@chromium.org>
---
kernel/time/Kconfig | 7 ++
kernel/time/Makefile | 1 +
kernel/time/udelay_test.c | 170 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 178 insertions(+)
create mode 100644 kernel/time/udelay_test.c
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index f448513..c6af048 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -202,3 +202,10 @@ config HIGH_RES_TIMERS
endmenu
endif
+
+config UDELAY_TEST
+ tristate "udelay test driver"
+ default n
+ help
+ This builds the "udelay_test" module that helps to make sure
+ that udelay() is working properly.
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 57a413f..dca9175 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -12,3 +12,4 @@ 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_UDELAY_TEST) += udelay_test.o
diff --git a/kernel/time/udelay_test.c b/kernel/time/udelay_test.c
new file mode 100644
index 0000000..b89115f
--- /dev/null
+++ b/kernel/time/udelay_test.c
@@ -0,0 +1,170 @@
+/*
+ * 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, int iters)
+{
+ int min = 0, max = 0, fail_count = 0;
+ long long sum = 0;
+ long long avg;
+ int i;
+ /* Allow udelay to be up to 0.5% fast */
+ int allowed_error_ns = usecs * 5;
+
+ if (iters <= 0)
+ return 0;
+
+ 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;
+ 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) {
+ 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 <davidri...@chromium.org>");
+MODULE_LICENSE("GPL");
--
2.0.0.526.g5318336
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