linux-kernel - Re: [PATCH 2/2] printk: Add boottime and real timestamps

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Date:   Tue, 25 Jul 2017 15:00:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Mark Salyzyn <salyzyn@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Christoffer Dall <cdall@...aro.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Olof Johansson <olof@...om.net>, Theodore Ts'o <tytso@....edu>,
        Josh Poimboeuf <jpoimboe@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/2] printk: Add boottime and real timestamps

On Tue, Jul 25, 2017 at 08:17:27AM -0400, Prarit Bhargava wrote:
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5b1662ec546f..6cd38a25f8ea 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1,8 +1,8 @@
>  menu "printk and dmesg options"
>  
>  config PRINTK_TIME
> -	int "Show timing information on printks (0-1)"
> -	range 0 1
> +	int "Show timing information on printks (0-3)"
> +	range 0 3
>  	default "0"
>  	depends on PRINTK
>  	help
> @@ -13,7 +13,8 @@ config PRINTK_TIME
>  	  The timestamp is always recorded internally, and exported
>  	  to /dev/kmsg. This flag just specifies if the timestamp should
>  	  be included, not that the timestamp is recorded. 0 disables the
> -	  timestamp and 1 uses the local clock.
> +	  timestamp and 1 uses the local clock, 2 uses the monotonic clock, and
> +	  3 uses real clock.
>  
>  	  The behavior is also controlled by the kernel command line
>  	  parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst


choice
	prompt "printk default clock"
	default PRIMTK_TIME_DISABLE
	help
	 goes here

	config PRINTK_TIME_DISABLE
	bool "Disabled"
	help
	 goes here

	config PRINTK_TIME_LOCAL
	bool "local clock"
	help
	 goes here

	config PRINTK_TIME_MONO
	bool "CLOCK_MONOTONIC"
	help
	 goes here

	config PRINTK_TIME_REAL
	bool "CLOCK_REALTIME"
	help
	 goes here

endchoice

config PRINTK_TIME
	int
	default 0 if PRINTK_TIME_DISABLE
	default 1 if PRINTK_TIME_LOCAL
	default 2 if PRINTK_TIME_MONO
	default 3 if PRINTK_TIME_REAL


Although I must strongly discourage using REALTIME, DST will make
untangling your logs an absolute nightmare. I would simply not provide
it.