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

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Message-ID: <73fdb1d7-6333-be5e-46e6-20ac69ce2b7e@android.com>
Date:   Wed, 19 Jul 2017 11:13:26 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Prarit Bhargava <prarit@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     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 05:03 AM, Prarit Bhargava wrote:
>
> On 07/19/2017 03:23 AM, Thomas Gleixner wrote:
>> 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?
> 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.

Agreed, and so many tools will be in pain (toybox, busybox, for 
instance). Not that I disagree, but API changes should always get an 
environmental assessment ...

> Mark, why don't we get together and fixup my original patchset to make sure it
> meets your needs?  It will fix both of our issues albeit not necessarily in the
> text format you want it.
I am currently retesting with the rtc format patch rolled out 
separately, could probably roll into your set.

-- Mark