linux-kernel - Re: [patch 2/2] timekeeping: Always check for negative motion

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Message-ID: <CANDhNCrL_G+HPfKPNpH5QFhouE_Hn-Nx7EAC7vUjLeL580q-UQ@mail.gmail.com>
Date: Fri, 1 Nov 2024 21:15:34 -0700
From: John Stultz <jstultz@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, 
	Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker <frederic@...nel.org>, 
	Stephen Boyd <sboyd@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch 2/2] timekeeping: Always check for negative motion

On Thu, Oct 31, 2024 at 5:04 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> clocksource_delta() has two variants. One with a check for negative motion,
> which is only selected by x86. This is a historic leftover as this function
> was previously used in the time getter hot paths.
>
> Since 135225a363ae timekeeping_cycles_to_ns() has unconditional protection
> against this as a by-product of the protection against 64bit math overflow.
>
> clocksource_delta() is only used in the clocksource watchdog and in
> timekeeping_advance(). The extra conditional there is not hurting anyone.
>
> Remove the config option and unconditionally prevent negative motion of the
> readout.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

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