linux-kernel - Re: [PATCH util-linux] dmesg: adjust timestamps according to suspended time

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Message-ID: <20200604102111.vst3goseqfxz5fa4@ws.net.home>
Date:   Thu, 4 Jun 2020 12:21:11 +0200
From:   Karel Zak <kzak@...hat.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     util-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH util-linux] dmesg: adjust timestamps according to
 suspended time

On Thu, Jun 04, 2020 at 12:43:52PM +0300, Konstantin Khlebnikov wrote:
> On 04/06/2020 12.30, Karel Zak wrote:
> > On Mon, Jun 01, 2020 at 10:21:34PM +0300, Konstantin Khlebnikov wrote:
> > > Timestamps in kernel log comes from monotonic clocksource which does not
> > > tick when system suspended. Suspended time easily sums into hours and days
> > > rendering human readable timestamps in dmesg useless.
> > > 
> > > Adjusting timestamps accouring to current delta between boottime and
> > > monotonic clocksources produces accurate timestamps for messages printed
> > > since last resume. Which are supposed to be most interesting.
> > 
> > It's definitely better than the current broken timestamps, but the real
> > and final solution is to have exact information about system suspends.
> > 
> > It would be enough to maintain in kernel memory a simple log with
> >     <bootime> <monotonic> <state_change>
> > and export this info by /proc/suspendlog, after that we can all
> > re-count /dev/kmsg timestamps to something useful.
> 
> Boottime or real time could be simply printed into kernel log at
> suspend and resume. So demsg could detect current offset while reading.

 Yes, but not sure if this is the most robust way (dmesg --clear will
 remove this info) and I guess the suspendlog can be useful
 independently on kmsg.

    Karel

-- 
 Karel Zak  <kzak@...hat.com>
 http://karelzak.blogspot.com