This change adds a module and a script that makes use of it to
validate that udelay delays for at least as long as requested
(as compared to ktime).
Changes since v1:
- allow udelay() to be 0.5% faster than requested as per feedback
Changes since v2:
- fix permissions on udelay_test.sh script
- update commit message to indicate what this test targets
- fixed checkpatch whitespace error
- rebased
Changes since v3:
- fixed xtensa compile warning (and other 32-bit platforms which
use the generic do_div)
- renamed and moved config option
David Riley (2):
kernel: time: Add udelay_test module to validate udelay
tools: add script to test udelay
kernel/time/Makefile | 1 +
kernel/time/udelay_test.c | 168 ++++++++++++++++++++++++++++++++++++++++++++++
lib/Kconfig.debug | 9 +++
tools/time/udelay_test.sh | 66 ++++++++++++++++++
4 files changed, 244 insertions(+)
create mode 100644 kernel/time/udelay_test.c
create mode 100755 tools/time/udelay_test.sh
--
2.0.0
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 <[email protected]>
---
kernel/time/Makefile | 1 +
kernel/time/udelay_test.c | 168 ++++++++++++++++++++++++++++++++++++++++++++++
lib/Kconfig.debug | 9 +++
3 files changed, 178 insertions(+)
create mode 100644 kernel/time/udelay_test.c
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 57a413f..5b2dc10 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_TEST_UDELAY) += udelay_test.o
diff --git a/kernel/time/udelay_test.c b/kernel/time/udelay_test.c
new file mode 100644
index 0000000..e622ba3
--- /dev/null
+++ b/kernel/time/udelay_test.c
@@ -0,0 +1,168 @@
+/*
+ * 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 <[email protected]>");
+MODULE_LICENSE("GPL");
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ccca322..d15a2a1 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1635,6 +1635,15 @@ config TEST_USER_COPY
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"
--
2.0.0
This script makes use of the udelay_test module to exercise udelay()
and ensure that it is delaying long enough (as compared to ktime).
Signed-off-by: David Riley <[email protected]>
---
tools/time/udelay_test.sh | 66 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 66 insertions(+)
create mode 100755 tools/time/udelay_test.sh
diff --git a/tools/time/udelay_test.sh b/tools/time/udelay_test.sh
new file mode 100755
index 0000000..12d46b9
--- /dev/null
+++ b/tools/time/udelay_test.sh
@@ -0,0 +1,66 @@
+#!/bin/bash
+
+# udelay() test script
+#
+# Test is executed by writing and reading to /sys/kernel/debug/udelay_test
+# and exercises a variety of delays to ensure that udelay() is delaying
+# at least as long as requested (as compared to ktime).
+#
+# 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.
+
+MODULE_NAME=udelay_test
+UDELAY_PATH=/sys/kernel/debug/udelay_test
+
+setup()
+{
+ /sbin/modprobe -q $MODULE_NAME
+ tmp_file=`mktemp`
+}
+
+test_one()
+{
+ delay=$1
+ echo $delay > $UDELAY_PATH
+ tee -a $tmp_file < $UDELAY_PATH
+}
+
+cleanup()
+{
+ if [ -f $tmp_file ]; then
+ rm $tmp_file
+ fi
+ /sbin/modprobe -q -r $MODULE_NAME
+}
+
+trap cleanup EXIT
+setup
+
+# Delay for a variety of times.
+# 1..200, 200..500 (by 10), 500..2000 (by 100)
+for (( delay = 1; delay < 200; delay += 1 )); do
+ test_one $delay
+done
+for (( delay = 200; delay < 500; delay += 10 )); do
+ test_one $delay
+done
+for (( delay = 500; delay <= 2000; delay += 100 )); do
+ test_one $delay
+done
+
+# Search for failures
+count=`grep -c FAIL $tmp_file`
+if [ $? -eq "0" ]; then
+ echo "ERROR: $count delays failed to delay long enough"
+ retcode=1
+fi
+
+exit $retcode
--
2.0.0
Thanks for the fixups. I've requeued these for 3.17.
thanks
-john
On Mon, Jun 16, 2014 at 2:58 PM, David Riley <[email protected]> wrote:
> This change adds a module and a script that makes use of it to
> validate that udelay delays for at least as long as requested
> (as compared to ktime).
>
> Changes since v1:
> - allow udelay() to be 0.5% faster than requested as per feedback
>
> Changes since v2:
> - fix permissions on udelay_test.sh script
> - update commit message to indicate what this test targets
> - fixed checkpatch whitespace error
> - rebased
>
> Changes since v3:
> - fixed xtensa compile warning (and other 32-bit platforms which
> use the generic do_div)
> - renamed and moved config option
>
> David Riley (2):
> kernel: time: Add udelay_test module to validate udelay
> tools: add script to test udelay
>
> kernel/time/Makefile | 1 +
> kernel/time/udelay_test.c | 168 ++++++++++++++++++++++++++++++++++++++++++++++
> lib/Kconfig.debug | 9 +++
> tools/time/udelay_test.sh | 66 ++++++++++++++++++
> 4 files changed, 244 insertions(+)
> create mode 100644 kernel/time/udelay_test.c
> create mode 100755 tools/time/udelay_test.sh
>
> --
> 2.0.0
>