linux-kernel - Re: [PATCH] printk, allow different timestamps for printk.time [v2]

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Message-ID: <56AA14F6.7060802@redhat.com>
Date:	Thu, 28 Jan 2016 08:17:42 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	Vasily Averin <vvs@...tuozzo.com>, linux-kernel@...r.kernel.org
CC:	John Stultz <john.stultz@...aro.org>,
	Xunlei Pang <pang.xunlei@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Baolin Wang <baolin.wang@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Petr Mladek <pmladek@...e.cz>, Tejun Heo <tj@...nel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH] printk, allow different timestamps for printk.time [v2]

On 01/28/2016 07:52 AM, Vasily Averin wrote:
> Dear Prarit,
> 

Hi Vasily,  Thanks for your suggestions.

> I have no objections about your patch,
> bit in fact I doubt we really need to convert each timestamp in kernel logs.
> How do you think is it probably better to convert only one timestamp per screen ?

How do you measure a screen? :)

> I.e. convert it in each 25th string only?

While your suggestion does work for a flood of messages this will miss
situations where an event occurred hours/minutes/seconds earlier leading to a
panic.

> Or just do it once per N seconds?

I've tried several other versions of the patch and other userspace options (such
as "date +%N > /tmp/kmsg" every second, setting up a timer to dump the real
time,  etc.).  Assuming that the disks didn't die (which was also part of the
problem I have seen) the printk buffer is finite in size and it is easy to fill
the buffer if you're not careful.

> And do not replace original timestamp but add converted one?

I'm not sure I see the benefit of having two timestamps but if someone really
wanted that I could add an additional patch to do it.

At the end of the day I need to be able to determine in real time what happened
on a system and to make that as easy as possible for a human to read.

P.