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Subject: Re: [PATCH 3/3 v11] printk: Add monotonic, boottime, and realtime
 timestamps
To: Prarit Bhargava <prarit@redhat.com>, linux-kernel@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        John Stultz <john.stultz@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stephen Boyd <sboyd@codeaurora.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Christoffer Dall <cdall@linaro.org>,
        Deepa Dinamani <deepa.kernel@gmail.com>,
        Ingo Molnar <mingo@kernel.org>, Joel Fernandes <joelaf@google.com>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        "Luis R. Rodriguez" <mcgrof@kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Olof Johansson <olof@lixom.net>, Josh Poimboeuf <jpoimboe@redhat.com>,
        linux-doc@vger.kernel.org
References: <1504613201-23868-1-git-send-email-prarit@redhat.com>
 <1504613201-23868-4-git-send-email-prarit@redhat.com>
From: Mark Salyzyn <salyzyn@android.com>
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Date: Wed, 13 Sep 2017 11:30:51 -0700
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On 09/05/2017 05:06 AM, Prarit Bhargava wrote:
> printk.time=1/CONFIG_PRINTK_TIME=1 adds a unmodified local hardware clock
> timestamp to printk messages.  The local hardware clock loses time each
> day making it difficult to determine exactly when an issue has occurred in
> the kernel log, and making it difficult to determine how kernel and
> hardware issues relate to each other in real time.
>
> Make printk output different timestamps by adding options for no
> timestamp, the local hardware clock, the monotonic clock, the boottime
> clock, and the real clock.  Allow a user to pick one of the clocks by
> using the printk.time kernel parameter.  Output the type of clock in
> /sys/module/printk/parameters/time so userspace programs can interpret the
> timestamp.
>
> v2: Use peterz's suggested Kconfig options.  Merge patchset together.
> Fix i386 !CONFIG_PRINTK builds.
>
> v3: Fixed x86_64_defconfig. Added printk_time_type enum and
> printk_time_str for better output. Added BOOTTIME clock functionality.
>
> v4: Fix messages, add additional printk.time options, and fix configs.
>
> v5: Renaming of structures, and allow printk_time_set() to
> evaluate substrings of entries (eg: allow 'r', 'real', 'realtime').  From
> peterz, make fast functions return 0 until timekeeping is initialized
> (removes timekeeping_active & ktime_get_boot|real_log_ts() suggested by
>   tglx and adds ktime_get_real_offset()).  Switch to a function pointer
> for printk_get_ts() and reference fast functions.  Make timestamp_sources enum
> match choice options for CONFIG_PRINTK_TIME (adds PRINTK_TIME_UNDEFINED).
>
> v6: Define PRINTK_TIME_UNDEFINED for !CONFIG_PRINTK builds.  Separate
> timekeeping changes into separate patch.  Minor include file cleanup.
>
> v7: Add default case to printk_set_timestamp() and add PRINTK_TIME_DEBUG
> for users that want to set timestamp to different values during runtime.
> Add jstultz' Kconfig to avoid defconfig churn.
>
> v8: Add CONFIG_PRINTK_TIME_DEBUG to allow timestamp runtime switching.
> Rename PRINTK_TIME_DISABLE to PRINTK_TIME_DISABLED.  Rename
> printk_set_timestamp() to printk_set_ts_func().  Separate
> printk_set_ts_func() and printk_get_first_ts() portions.  Rename param
> functions.  Adjust configs, enum, and timestamp_sources_str to be 0-4.
> Add mention realtime clock is UTC in Documentation.
>
> v9: Fix typo.  Add __ktime_get_real_fast_ns_unsafe().
>
> v10: Remove time parameter restrictions.
>
Ack and unit tested on Backport to 4.9.

(you are missing the v11 respin comment, NBD)

-- Mark