netdev - Re: [patch V3 04/11] timekeeping: Provide time setter for auxiliary clocks

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Message-ID: <87ldpdnu8y.ffs@tglx>
Date: Fri, 27 Jun 2025 16:18:05 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: John Stultz <jstultz@...gle.com>
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 V3 04/11] timekeeping: Provide time setter for auxiliary
 clocks

On Thu, Jun 26 2025 at 21:23, John Stultz wrote:
> On Wed, Jun 25, 2025 at 11:38 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>>
>> Add clock_settime(2) support for auxiliary clocks. The function affects the
>> AUX offset which is added to the "monotonic" clock readout of these clocks.
>>
>> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>> ---
>
> Minor fretting: I worry a little that the difference here between the
> default timekeeper where set adjusts the REALTIME offset from
> MONOTONIC, and here where it directly adjusts "mono" might confuse
> later readers?

Actually it's not really that different.

In both cases the new offset to the monotonic clock is calculated and
stored in the relevant tk::offs_* member.

The difference is that the core timekeeper operates on xtime, but for
simplicity I chose to calculate the resulting tk::offs_aux directly from
the monotonic base. That's valid with the aux clocks as they don't
need any of the xtime parts.

I added some blurb to it.