linux-kernel - Re: [PATCH v5] printk: Add pr_info_show

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Date:   Fri, 21 Jul 2017 04:00:57 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     linux-kernel@...r.kernel.org, pavel@....cz,
        andriy.shevchenko@...ux.intel.com, joe@...ches.com,
        prarit@...hat.com, rjw@...ysocki.net, tglx@...utronix.de,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Mark Salyzyn <salyzyn@...gle.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Olof Johansson <olof@...om.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v5] printk: Add pr_info_show_time

On Thu, Jul 20, 2017 at 11:24:22AM -0700, Mark Salyzyn wrote:
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 98fe715522e8..0d63c3fb4e24 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -30,6 +30,58 @@ config CONSOLE_LOGLEVEL_DEFAULT
>  	  usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT
>  	  option.
>  
> +# set if time is being printed in pr_info_show_time()
> +config PR_INFO_SHOW_TIME
> +	bool
> +
> +choice
> +	prompt "pr_info_show_time() alternate time message prefix"
> +	help
> +	  Activate alternate time prefix in pr_info_show_time
> +
> +	  The primary use of the instrumentation is to aid field
> +	  analysis of Battery and Power usage.  The instrumentation
> +	  may also help triage and synchronize kernel logs and user
> +	  space activity logs at key displacements.
> +	config PR_INFO_SHOW_TIME_MONOTONIC
> +		bool "monotonic"
> +		help
> +		  Deactivate alternate time prefix in pr_info_show_time.
> +		  Doing so because monotonic time is part of the normal
> +		  printk time logging.
> +
> +		  Print only the supplied message in pr_info_show_time,
> +		  indistinguishable from pr_info.
> +	config PR_INFO_SHOW_TIME_REALTIME
> +		bool "realtime"
> +		select PR_INFO_SHOW_TIME
> +		help
> +		  Activate alternate time prefix in pr_info_show_time
> +
> +		  The primary use of the instrumentation is to aid field
> +		  analysis of Battery and Power usage.  The instrumentation
> +		  may also help triage and synchronize kernel logs and user
> +		  space activity logs at key displacements.  For instance
> +		  CLOCK_MONOTONIC stops while suspended, while CLOCK_REALTIME
> +		  continues, and the timestamps help re-orient post-analysis.
> +
> +		  Prefix realtime [<epoch>.<ns>U] timestamp in pr_info_show_time
> +	config PR_INFO_SHOW_TIME_BOOTTIME
> +		bool "boottime"
> +		select PR_INFO_SHOW_TIME
> +		help
> +		  Activate alternate time prefix in pr_info_show_time
> +
> +		  The primary use of the instrumentation is to aid field
> +		  analysis of Battery and Power usage.  The instrumentation
> +		  may also help triage and synchronize kernel logs and user
> +		  space activity logs at key displacements.  For instance
> +		  CLOCK_MONOTONIC stops while suspended, while CLOCK_BOOTTIME
> +		  continues, and the timestamps help re-orient post-analysis.
> +
> +		  Prefix boottime [<epoch>.<ns>B] timestamp in pr_info_show_time
> +endchoice

There is no depends magic anywhere here, so none of this actually has complex
dependencies, this is just boot time preference setup, and for that I think a
boot param and sysctl value could easily not only enable the same but *also*
enable run time ability to swap between these. Even for the branch performance
consideration can't jump labels be used to address that if there is a concern
for that?

I think that would also make the code easier to read and remove all this kconfig
extra stuff. Then its just a run time thing.

Also, should there be no checks for time being available and ready before this
is used?

  Luis