Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.32 as permitted sender) client-ip=23.128.96.32;
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     Anna-Maria Behnsen <anna-maria@linutronix.de>,
        linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        John Stultz <jstultz@google.com>,
        Eric Dumazet <edumazet@google.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Arjan van de Ven <arjan@infradead.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Rik van Riel <riel@surriel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sebastian Siewior <bigeasy@linutronix.de>,
        Giovanni Gherdovich <ggherdovich@suse.cz>,
        Lukasz Luba <lukasz.luba@arm.com>,
        "Gautham R . Shenoy" <gautham.shenoy@amd.com>,
        Srinivas Pandruvada <srinivas.pandruvada@intel.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>
Subject: Re: [PATCH v8 08/25] timer: Rework idle logic
In-Reply-To: <ZSUzJpeT86pQ8YcY@lothringen>
References: <20231004123454.15691-1-anna-maria@linutronix.de>
 <20231004123454.15691-9-anna-maria@linutronix.de> <878r8bphn6.ffs@tglx>
 <ZSUzJpeT86pQ8YcY@lothringen>
Date:   Tue, 10 Oct 2023 13:48:50 +0200
Message-ID: <87ttqyofz1.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Tue, Oct 10 2023 at 13:19, Frederic Weisbecker wrote:
> On Tue, Oct 10, 2023 at 12:15:09AM +0200, Thomas Gleixner wrote:
>> > +	base->is_idle = time_after(nextevt, basej + 1);
>> 
>> This is wrongly ordered. base->is_idle must be updated _after_
>> evaluating base->timers_pending because the below can change nextevt,
>> no?
>> 
>> > +	if (base->timers_pending) {
>> > +		/* If we missed a tick already, force 0 delta */
>> > +		if (time_before(nextevt, basej))
>> > +			nextevt = basej;
>> > +		expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
>
> I suspect it doesn't matter in pratice: base->is_idle will remain false
> if it's before/equal jiffies.
>
> Still it hurts the eyes so I agree the re-ordering should happen here and
> this will even simplify a bit the next patch.

Right. Anna-Maria just pointed that out to me before, but we are all in
violent agreement that it sucks :)