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Date: Thu, 4 Feb 2016 18:25:29 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
cc: Prarit Bhargava <prarit@redhat.com>, linux-kernel@vger.kernel.org,
        John Stultz <john.stultz@linaro.org>,
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Peter Hurley <peter@hurleysoftware.com>,
        Vasily Averin <vvs@virtuozzo.com>, Joe Perches <joe@perches.com>
Subject: Re: [PATCH] printk, allow different timestamps for printk.time
 [v2]
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On Thu, 4 Feb 2016, Petr Mladek wrote:
> On Thu 2016-01-28 07:43:49, Prarit Bhargava wrote:
> > +static u64 printk_get_ts(void)
> > +{
> > +	u64 mono, offset_real;
> > +
> > +	if (printk_time == 0)
> > +		return 0;
> > +
> > +	if (printk_time == 1)
> > +		return local_clock();
> > +
> > +	mono = ktime_get_log_ts(&offset_real);
> > +
> > +	if (printk_time == 2)
> > +		return mono;
> > +
> > +	return mono + offset_real;
> 
> At least dmesg is not capable to read the absolute size of the
> real time. It expects offset against the start of the timekeeping
> stuff or so. I get this:
> 
> $> dmesg | tail -n 5
> [    7.128924] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
> [    0.000000] printk: timestamp set to 0.
> [  179.983704] printk: timestamp set to 1.
> [  181.895655] printk: timestamp set to 2.
> [1454602412.026424] printk: timestamp set to 3.
> 
> $dmesg -T -S | tail -n 5
> [Thu Feb  4 17:10:34 2016] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
> [Thu Feb  4 17:10:27 2016] printk: timestamp set to 0.
> [Thu Feb  4 17:13:26 2016] printk: timestamp set to 1.
> [Thu Feb  4 17:13:28 2016] printk: timestamp set to 2.
> [Fri Mar 10 09:23:59 2062] printk: timestamp set to 3.
> 
> Please, note that the last entry points to the year 2062.

That's a problem of dmesg -T -S. It doesn't know that the timestamp (3) is
actually CLOCKTIME_REAL already:

-> 1454602412 / (3600 * 24 * 365)
 = 46.1251
-> 1970 + 46
 = 2016
 
Thanks,

	tglx