linux-kernel - Re: [PATCH v9 12/32] timers: Fix nextevt calculation when no timers are pending

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Message-ID: <875y13mu96.fsf@somnus>
Date:   Tue, 12 Dec 2023 14:21:25 +0100
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Sebastian Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <jstultz@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arjan van de Ven <arjan@...radead.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Lukasz Luba <lukasz.luba@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
        K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [PATCH v9 12/32] timers: Fix nextevt calculation when no timers
 are pending

Frederic Weisbecker <frederic@...nel.org> writes:

> Le Tue, Dec 05, 2023 at 12:53:03PM +0100, Anna-Maria Behnsen a écrit :
>> 
>> Frederic, what do you think?
>
> So it looks like is_idle must be fixed.
>
> As for the timer softirq, ->next_expiry is already unreliable because when
> a timer is removed, ->next_expiry is not updated (even though that removed
> timer might have been the earliest). So ->next_expiry can already carry a
> "too early" value. The only constraint is that ->next_expiry can't be later
> than the first timer.
>
> So I'd rather put a comment somewhere about the fact that wrapping is expected
> to behave ok. But it's your call.

Ok. If both solutions are fine, I would like to take the solution with
updating the next_expiry values for empty bases. It will make the
compare of expiry values of global and local timer base easier in one of
the patches later on.

Thanks,

	Anna-Maria