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Message-ID: <9496e1a6-d1-1a20-c1c9-2bc3f34eb888@linutronix.de>
Date: Tue, 8 Nov 2022 18:02:11 +0100 (CET)
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: Frederic Weisbecker <frederic@...nel.org>
cc: 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>,
Frederic Weisbecker <fweisbec@...il.com>,
Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v4 14/16] timer: Implement the hierarchical pull model
On Tue, 8 Nov 2022, Frederic Weisbecker wrote:
> On Fri, Nov 04, 2022 at 03:57:35PM +0100, Anna-Maria Behnsen wrote:
> > @@ -1859,6 +1863,36 @@ void forward_and_idle_timer_bases(unsigned long basej, u64 basem,
> > */
> > is_idle = time_after(nextevt, basej + 1);
> >
> > + if (is_idle) {
> > + u64 next_tmigr;
> > +
> > + next_tmigr = tmigr_cpu_deactivate(tevt->global);
> > +
> > + tevt->global = KTIME_MAX;
> > +
> > + /*
> > + * If CPU is the last going idle in timer migration
> > + * hierarchy, make sure CPU will wake up in time to handle
> > + * remote timers. next_tmigr == KTIME_MAX if other CPUs are
> > + * still active.
> > + */
> > + if (next_tmigr < tevt->local) {
> > + u64 tmp;
> > +
> > + /* If we missed a tick already, force 0 delta */
> > + if (next_tmigr < basem)
> > + next_tmigr = basem;
> > +
> > + tmp = div_u64(next_tmigr - basem, TICK_NSEC);
> > +
> > + nextevt = basej + (unsigned long)tmp;
> > + tevt->local = next_tmigr;
> > + is_idle = time_after(nextevt, basej + 1);
>
> So after that, tevt->global shouldn't matter anymore for tick_nohz_next_event(),
> right? If so then probably that line can go away (with a comment specifying why we can
> ignore the global part)?:
>
> tevt.local = min_t(u64, tevt.local, tevt.global);
>
tevt->global is set to KTIME_MAX anyway. So the whole tevt information is
also no longer required in tick_nohz_next_event(). I need to rework the
patch where this was introduced. Then the forward_and_idle_timer_bases()
could still simply return the next timer and then there is no longer a
point against using your idea with naming of the functions.
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