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Date: Thu, 14 Jan 2016 15:44:23 +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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        Baolin Wang <baolin.wang@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 0/2] printk, Add printk.clock kernel parameter [v2]
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On Thu, 14 Jan 2016, Petr Mladek wrote:
> On Wed 2016-01-13 18:28:50, Thomas Gleixner wrote:
> > You can solve the whole business by changing the timestamp in printk_log to
> > 
> >    u64	    mono;
> >    u64	    offset_real;
> 
> This is not so easy because the structure is proceed by userspace tool,
> e.g. crash, see log_buf_kexec_setup(). We would need to update all
> the tools as well.

Fair enough.
 
> > and have a function which does:
> > 
> > u64 ktime_get_log_ts(u64 *offset_real)
> > {
> > 	*offset_real = tk_core.timekeeper.offs_real;
> > 
> > 	if (timekeeping_active)
> > 		return ktime_get_mono_fast_ns();
> > 	else
> > 		return local_clock();
> > }
> 
> A solution would be to apply the offset_real immediately. I wonder if
> any tool expects the messages to be sorted by a monotonic clock. In
> fact, it might be useful to see that some messages are disordered
> against the real time, e.g. because of the leaf second.

Not only leap seconds, it's also settimeofday and NTP might make the wall time
jump under certain conditions.

Thanks,

	tglx