linux-kernel - Re: [PATCH 0/2 v6] printk, Add monotonic and real printk timestamps

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Date:	Thu, 10 Mar 2016 11:00:12 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	John Stultz <john.stultz@...aro.org>,
	Xunlei Pang <pang.xunlei@...aro.org>,
	Baolin Wang <baolin.wang@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tejun Heo <tj@...nel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	Vasily Averin <vvs@...tuozzo.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 0/2 v6] printk, Add monotonic and real printk timestamps

On Tue 2016-03-08 06:03:24, Prarit Bhargava wrote:
> 
> 
> On 03/08/2016 02:59 AM, Thomas Gleixner wrote:
> > On Tue, 23 Feb 2016, Prarit Bhargava wrote:
> > 
> >> This patchset adds monotonic and real printk timestamps.  The first patch
> >> changes CONFIG_PRINT_TIME from a bool to an int to allow for the additional
> >> timestamps that are added in patch 2.
> >>
> >> Changes from v6: Petr Mladek pointed out that the current patch
> >> fails to indicate to userspace programs which timestamp is being used.
> > 
> > How is that solved?
> 
> Hi Thomas,
> 
> Userspace programs can now look at /sys/modules/printk/parameters/time which
> will contain [0-3] for the timestamp clock.

But it includes only the current setting that is valid only for
messages printed with this setting. The ring buffer might include
different messages produced with different setting.

I suggest to look how dmesg handles the time stamp. I wonder how it
converts the relative time into an absolute one. I wonder if you
could convert all timestamps to the relative format, so that you
do not need to change all userspace tools at all.

Best regards,
Petr