linux-kernel - Re: [PATCH v2 1/2] time/timekeeping: Fix possible inconsistencies in

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Message-ID: <CANDhNCo82jKs4Tq8uiqmJvT5JyPw8VQPFg526POooK0O+15-uQ@mail.gmail.com>
Date: Wed, 16 Apr 2025 19:55:55 -0700
From: John Stultz <jstultz@...gle.com>
To: Miroslav Lichvar <mlichvar@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>, 
	Stephen Boyd <sboyd@...nel.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Frederic Weisbecker <frederic@...nel.org>, Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org, 
	kernel-team@...roid.com, Lei Chen <lei.chen@...rtx.com>
Subject: Re: [PATCH v2 1/2] time/timekeeping: Fix possible inconsistencies in
 _COARSE clockids

On Mon, Mar 31, 2025 at 12:54 AM Miroslav Lichvar <mlichvar@...hat.com> wrote:
> On Thu, Mar 27, 2025 at 06:32:27PM +0100, Thomas Gleixner wrote:
> > On Thu, Mar 27 2025 at 16:42, Miroslav Lichvar wrote:
> > > On Thu, Mar 27, 2025 at 10:22:31AM +0100, Thomas Gleixner wrote:
> > > To clearly see the difference with the new code, I made an attempt
> > > to update the old linux-tktest simulation that was used back when the
> > > multiplier adjustment was reworked, but there are too many missing
> > > things now and I gave up.
> >
> > Can you point me to that code?
>
> It's this thing: https://github.com/mlichvar/linux-tktest
>
> > It would be probably useful to create a test mechanism which allows to
> > exercise all of this in a simulated way so we actually don't have to
> > wonder every time we change a bit what the consequences are.
>
> Yes, that would be very nice if we could run the timekeeping code in a
> deterministic simulated environment with a configurable clocksource,
> timing of kernel updates, timing and values of injected adjtimex()
> calls, etc. The question is how to isolate it.

Miroslav, Have you looked at KUNIT?
https://docs.kernel.org/dev-tools/kunit/index.html

I've not yet done much with it, but it seems like it might be a good
match for moving some of this simulation logic (which has always
impressed me) into the kernel tree.

thanks
-john