Re: [PATCH v2 1/4] time: rtc-lib: Add rtc_show_time(const char *prefix_msg)

[Thomas Gleixner]

On Tue, 18 Jul 2017, Mark Salyzyn wrote:
> On 07/18/2017 03:35 PM, Thomas Gleixner wrote:
> > There was some discussion about making the clock source for dmesg time
> > stamps selectable, so you can use MONOTONIC, REALTIME, BOOTTIME. The
> > patches looked sensible, but there was some showstopper vs. the user space
> > dmesg utility. See:
> 
> The timestamps are useful for the 'second' purpose of these patches when
> dmesg time is BOOTTIME or MONOTONIC, and can be turned off if REALTIME
> is selected. Having rtc_show_time a single point for switching this no doubt
> helps,
> not hinders, that dmesg issue.
> 
> The inflection points would still serve a purpose, still need
> suspend/resume/hibernate/restore. The reboot messages are _only_ useful to
> us with their timestamps, as I checked and the only tools that use those are
> for log synchronization. We may be able to do away with them on REALTIME
> dmesg'ing; but the standardization of the message as a marker would have a
> legacy purpose (!)
> 
> NB: We have a similar configuration for the user space logger, which can be
> configured to report in MONOTONIC time. We have yet to have a vendor
> use the feature, opting for REALTIME logging for user space activities.
> Our klogd (which runs at background priority and is batched) manages a
> histogram relationship between MONOTONIC and REALTIME helped by these
> prints and incorporates the REALTIME dmesg logs merged into our user
> space logging database.

There is another option to remedy this and the dmesg tooling issues:

Instead of switching the time stamps in dmesg to a different clock we might
as well have an optional secondary timestamp. So instead of:

 [  341.590930] wlan0: associated

you would get:

 [  341.590930] [ sec.usec] wlan0: associated

where the second time stamp would be CLOCK_REALTIME/BOOTTIME.

That should also solve Prarits problem, hmm?

Thanks,

	tglx