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

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Message-ID: <3ac0a334-6779-535a-dfe1-086ae7333bda@android.com>
Date:   Tue, 25 Jul 2017 15:39:16 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, 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 07/25/2017 06:00 AM, Peter Zijlstra wrote:
> 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.

I agree with using select, ensures only valid values are landed. It does 
mean that CONFIG_PRINTK_TIME in-effect gets deprecated.

REALTIME is always UTC in the kernel.

What about BOOTTIME?

-- Mark