linux-kernel - Re: [patch V2 15/26] timekeeping: Add AUX offset to struct timekeeper

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Message-ID: <CANDhNCrMBaHhyrr3=kq=nyAp2iGhkJgKMqwO8+KeeYaZdbSa3A@mail.gmail.com>
Date: Fri, 13 Jun 2025 19:44:02 -0700
From: John Stultz <jstultz@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org, 
	Richard Cochran <richardcochran@...il.com>, Christopher Hall <christopher.s.hall@...el.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Miroslav Lichvar <mlichvar@...hat.com>, Werner Abt <werner.abt@...nberg-usa.com>, 
	David Woodhouse <dwmw2@...radead.org>, Stephen Boyd <sboyd@...nel.org>, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
	Kurt Kanzenbach <kurt@...utronix.de>, Nam Cao <namcao@...utronix.de>, 
	Antoine Tenart <atenart@...nel.org>
Subject: Re: [patch V2 15/26] timekeeping: Add AUX offset to struct timekeeper

On Mon, May 19, 2025 at 1:33 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> This offset will be used in the time getters of auxiliary clocks. It is
> added to the "monotonic" clock readout.
>
> As auxiliary clocks do not utilize the offset fields of the core time
> keeper, this is just an alias for offs_tai, so that the cache line layout
> stays the same.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/timekeeper_internal.h |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> ---
> --- a/include/linux/timekeeper_internal.h
> +++ b/include/linux/timekeeper_internal.h
> @@ -67,6 +67,7 @@ struct tk_read_base {
>   * @offs_real:                 Offset clock monotonic -> clock realtime
>   * @offs_boot:                 Offset clock monotonic -> clock boottime
>   * @offs_tai:                  Offset clock monotonic -> clock tai
> + * @offs_aux:                  Offset clock monotonic -> clock AUX
>   * @coarse_nsec:               The nanoseconds part for coarse time getters
>   * @id:                                The timekeeper ID
>   * @tkr_raw:                   The readout base structure for CLOCK_MONOTONIC_RAW
> @@ -139,7 +140,10 @@ struct timekeeper {
>         struct timespec64       wall_to_monotonic;
>         ktime_t                 offs_real;
>         ktime_t                 offs_boot;
> -       ktime_t                 offs_tai;
> +       union {
> +               ktime_t         offs_tai;
> +               ktime_t         offs_aux;
> +       };

Probably could use a clarifying comment similar to what you have in
the commit message "auxiliary clocks do not utilize the offset fields
of the core time keeper"

Otherwise,
 Acked-by: John Stultz <jstultz@...gle.com>

thanks
-john