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

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Date:	Thu, 28 Jan 2016 16:49:47 +0300
From:	Vasily Averin <vvs@...tuozzo.com>
To:	Prarit Bhargava <prarit@...hat.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 28.01.2016 16:17, Prarit Bhargava wrote:
> 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 mean 80x25, but you're right, it makes sense to do it configurable.

>> 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.

I investigate periodically various "node hangs" issues,
without saved vmcore, /var/log/messages, net or serial console.
All what I have is screenshot on local console, in worst case 80x25.

I'm ready to lose ~10 characters on each string for short timesetamp,
and of course I would be happy to know real date of these messages.
But for me it's enough to see full date once per screen, 
and have short relative timestamp on other strings.

> 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.
>