From: Jan Engelhardt <jengelh@linux01.gwdg.de>

Currently, enabling/disabling printk timestamps is only possible through
reboot (bootparam) or recompile.  I normally do not run with timestamps
(since syslog handles that in a good manner), but for measuring small
kernel delays (e.g.  irq probing - see parport thread) I needed subsecond
precision, but then again, just for some minutes rather than all kernel
messages to come.  The following patch adds a module_param() with which the
timestamps can be en-/disabled in a live system through
/sys/modules/printk/parameters/printk_time.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 kernel/printk.c |    2 ++
 1 file changed, 2 insertions(+)

diff -puN kernel/printk.c~printk-time-parameter kernel/printk.c
--- a/kernel/printk.c~printk-time-parameter
+++ a/kernel/printk.c
@@ -24,6 +24,7 @@
 #include <linux/console.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/moduleparam.h>
 #include <linux/interrupt.h>			/* For in_interrupt() */
 #include <linux/config.h>
 #include <linux/delay.h>
@@ -439,6 +440,7 @@ static int printk_time = 1;
 #else
 static int printk_time = 0;
 #endif
+module_param(printk_time, int, S_IRUGO | S_IWUSR);
 
 static int __init printk_time_setup(char *str)
 {
_