Re: [PATCH v2] printk: Add boottime and real timestamps

[John Stultz]

On Tue, Aug 1, 2017 at 5:55 AM, Prarit Bhargava <prarit@xxxxxxxxxx> 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 timestampes by adding options for no
> timestamp, the local hardware clock, the monotonic 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.
>
> Real clock & 32-bit systems:  Selecting the real clock printk timestamp may
> lead to unlikely situations where a timestamp is wrong because the real time
> offset is read without the protection of a sequence lock in the call to
> ktime_get_log_ts() in printk_get_ts().
>
> v2: Use peterz's suggested Kconfig options.  Merge patchset together.  Fix
> i386 !CONFIG_PRINTK builds.
>
> Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
...
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 98fe715522e8..7a8870b4ddbb 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1,8 +1,39 @@
>  menu "printk and dmesg options"
>
> +choice
> +       prompt "printk default clock"
> +       config PRINTK_TIME_DISABLE
> +       bool "Disabled"
> +       help
> +        Selecting this option disables the time stamps of printk().
> +
> +       config PRINTK_TIME_LOCAL
> +       bool "Local Clock"
> +       help
> +         Selecting this option causes the time stamps of printk() to be
> +         stamped with the unadjusted hardware clock.
> +
> +       config PRINTK_TIME_MONO
> +       bool "CLOCK_MONOTONIC"
> +       help
> +         Selecting this option causes the time stamps of printk() to be
> +         stamped with the adjusted monotonic clock.
> +
> +       config PRINTK_TIME_REAL
> +       bool "CLOCK_REALTIME"
> +       help
> +         Selecting this option causes the time stamps of printk() to be
> +         stamped with the adjusted realtime clock.

Its been asked already, but I've not yet seen an answer.
Is there a reason your not also adding PRINTK_TIME_BOOT here (which to
me would be more generally useful then REAL or MONO)?

thanks
-john