linux-kernel - Re: [PATCH v2 1/4] time: rtc-lib: Add rtc_show_time(const char *prefix

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Message-ID: <abb4ef30-06c2-18db-6c8d-c29be1b1fa3d@redhat.com>
Date:   Wed, 19 Jul 2017 10:28:04 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Mark Salyzyn <salyzyn@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>, rjw@...ysocki.net,
        len.brown@...el.com, pavel@....cz, linux-pm@...r.kernel.org,
        a.zummo@...ertech.it, alexandre.belloni@...e-electrons.com,
        linux-rtc@...r.kernel.org, andy.shevchenko@...il.com,
        Mark Salyzyn <salyzyn@...gle.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thierry Strudel <tstrudel@...gle.com>,
        John Stultz <john.stultz@...aro.org>,
        Richard Cochran <richardcochran@...il.com>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 1/4] time: rtc-lib: Add rtc_show_time(const char
 *prefix_msg)

On 07/19/2017 08:28 AM, Thomas Gleixner wrote:
> On Wed, 19 Jul 2017, Prarit Bhargava wrote:
>> On 07/19/2017 03:23 AM, Thomas Gleixner wrote:
>>> 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?
>>
>> It would but I would prefer a single time stamp be printed than two.  I think
>> two timestamps is adding confusion to the output from a end-users point of view.
> 
> Fair enough. I came up with that idea when I looked at the old thread. The
> discussion about tools (e.g. dmesg) dried out at some point and looked
> unresolved.

tglx,

There were two outstanding issues with my patchset.  The first, as you mention
above, is the issue with tooling.  I will handle the chicken-and-egg issue with
the kernel modification and tooling.  I will post patches for dmesg & systemd
once the kernel patchset lands in a "next" tree; other tools will have to be
patched as we find them.

The second issue is a sysfs stability and output issue that I have a question
on.  Since I'm changing the value of print.time from a bool to an int, the
output of /sys/modules/printk/parameters/time would change from Y/N to 0-3.  The
file is not listed in Documentation/ABI/stable so I think I can change it.  Can
you confirm that this is the case?  I wary of changing anything under sysfs and
I'm not sure who else would know if I can change the output of that file.

If it is the case that the output can be changed, then I'm going to suggest that
we allow, for example, human-readable format "printk.time=monotonic" along with
"printk.time=2" as kernel parameters.  I would also like your thoughts on that idea.

If the file cannot be changed I will have to add an additional module parameter
to printk.  Does "timestamp" sound okay to you?  I will go with whatever you
suggest.

Thanks,

P.