Over the past years I've seen many reports of bugs that include time-stamped kernel logs (enabled when CONFIG_PRINTK_TIME=y or print.time=1 is specified as a kernel parameter) that do not align with either external time stamped logs or /var/log/messages.
For example, [root@intel-wildcatpass-06 ~]# date; echo "Hello!" > /dev/kmsg ; date Thu Dec 17 13:58:31 EST 2015 Thu Dec 17 13:58:31 EST 2015 which displays [83973.768912] Hello! on the serial console. Running a script to convert this to "boot time", [root@intel-wildcatpass-06 ~]# ./human.sh | tail -1 [Thu Dec 17 13:59:57 2015] Hello! which is already off by 1 minute and 26 seconds off after ~24 hours of uptime. This occurs because the time stamp is obtained from a call to local_clock() which (on x86) is a direct call to the hardware. These hardware clock reads are not modified by the standard ntp or ptp protocol, while the other timestamps are, and that results in situations where /var/log/messages timestamps are further and further offset from the hardware clock timestamps. This patch introduces printk.clock=[local|boot|real|tai] allowing a user to specify an adjusted clock to use with printk timestamps. The hardware clock, or the existing functionality, is preserved by default. Cc: John Stultz <[email protected]> Cc: Xunlei Pang <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Baolin Wang <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Petr Mladek <[email protected]> Cc: Tejun Heo <[email protected]> Cc: Peter Hurley <[email protected]> Cc: Vasily Averin <[email protected]> Cc: Joe Perches <[email protected]> Signed-off-by: Prarit Bhargava <[email protected]> Prarit Bhargava (2): kernel, timekeeping, add trylock option to ktime_get_with_offset() printk, Add printk.clock kernel parameter include/linux/time64.h | 2 + include/linux/timekeeping.h | 50 +++++++++++++++++++-- kernel/printk/printk.c | 105 +++++++++++++++++++++++++++++++++++++++---- kernel/time/timekeeping.c | 15 ++++++- 4 files changed, 159 insertions(+), 13 deletions(-) -- 1.7.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
