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>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>