From: Frederic Weisbecker <frederic@kernel.org>
To: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
John Stultz <jstultz@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
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>,
Frederic Weisbecker <fweisbec@gmail.com>,
Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH v4 14/16] timer: Implement the hierarchical pull model
Date: Tue, 29 Nov 2022 11:30:21 +0100 [thread overview]
Message-ID: <20221129103021.GB1706373@lothringen> (raw)
In-Reply-To: <20221128162010.GB1699488@lothringen>
On Mon, Nov 28, 2022 at 05:20:10PM +0100, Frederic Weisbecker wrote:
> On Thu, Nov 24, 2022 at 08:47:56AM +0100, Anna-Maria Behnsen wrote:
> > On Tue, 15 Nov 2022, Frederic Weisbecker wrote:
> >
> > > On Fri, Nov 04, 2022 at 03:57:35PM +0100, Anna-Maria Behnsen wrote:
> > > > +static int tmigr_cpu_offline(unsigned int cpu)
> > > > +{
> > > > + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu);
> > > > +
> > > > + raw_spin_lock_irq(&tmc->lock);
> > > > + tmc->online = 0;
> > > > + __tmigr_cpu_deactivate(tmc, KTIME_MAX);
> > >
> > > This means that if the CPU is going idle for some time during
> > > the hotplug process (ie: at some point between CPUHP_AP_TMIGR_ONLINE
> > > and CPUHP_TEARDOWN_CPU), then a global timer may be delayed for that long.
> > >
> > > I guess it shouldn't be too bad but worth mentioning...
> > >
> > > Although if it happens to be a problem it could be solved with simply allowing
> > > tmigr_cpu_deactivate() when !tmc->online.
> >
> > The plan was (and I broke it) to let the CPU handle global timers by itself
> > as long as timer migration hierarchy is not completely initialized and as
> > long as CPU is marked offline in timer migration hierarchy. Otherwise
> > global timers might be delayed during this period. The proper way would be
> > that tmigr_cpu_deactivate(nextexp) directly returns nextexp if !tmc->online
> > and tmigr hierarchy is not in place yet. I will have a deeper look if there
> > was a reason why I changed the return to KTIME_MAX...
>
> Well, do you need tmc->online at all?
>
> I guess tmigr_cpu_offline() could be simply removed because when the CPU goes
> finally down in do_idle() it does:
>
> tick_nohz_idle_stop_tick();
> cpuhp_report_idle_dead();
>
> So the tick is expected to be stopped (better check it is) and thus the tmc
> should be deactivated.
>
> I guess you just need to call tmigr_cpu_activate() from timers_prepare_cpu().
Now of course the issue is that between CPUHP_TIMERS_PREPARE and
CPUHP_AP_ONLINE_IDLE the tglobal timers may not be served.
One way to deal with that is to call tmigr_cpu_activate() from
cpu_startup_entry().
Otherwise then back to tmc->online I guess.
next prev parent reply other threads:[~2022-11-29 10:30 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-04 14:57 [PATCH v4 00/16] timer: Move from a push remote at enqueue to a pull at expiry model Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 01/16] tick-sched: Warn when next tick seems to be in the past Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 02/16] timer: Move store of next event into __next_timer_interrupt() Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 03/16] timer: Split next timer interrupt logic Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 04/16] timer: Rework idle logic Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 05/16] add_timer_on(): Make sure callers have TIMER_PINNED flag Anna-Maria Behnsen
2022-11-04 16:43 ` Frederic Weisbecker
2022-11-07 8:11 ` Anna-Maria Behnsen
2022-11-07 10:11 ` Frederic Weisbecker
2022-11-04 14:57 ` [PATCH v4 06/16] timer: Keep the pinned timers separate from the others Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 07/16] timer: Retrieve next expiry of pinned/non-pinned timers seperately Anna-Maria Behnsen
2022-11-07 11:58 ` Frederic Weisbecker
2022-11-04 14:57 ` [PATCH v4 08/16] timer: Rename get_next_timer_interrupt() Anna-Maria Behnsen
2022-11-07 12:13 ` Frederic Weisbecker
2022-11-04 14:57 ` [PATCH v4 09/16] timer: Split out "get next timer interrupt" functionality Anna-Maria Behnsen
2022-11-07 12:42 ` Frederic Weisbecker
2022-11-08 15:30 ` Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 10/16] timer: Add get next timer interrupt functionality for remote CPUs Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 11/16] timer: Restructure internal locking Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 12/16] timer: Check if timers base is handled already Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 13/16] tick/sched: Split out jiffies update helper function Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 14/16] timer: Implement the hierarchical pull model Anna-Maria Behnsen
2022-11-07 22:07 ` Frederic Weisbecker
2022-11-08 16:16 ` Anna-Maria Behnsen
2022-11-09 17:12 ` Frederic Weisbecker
2022-11-08 10:47 ` Frederic Weisbecker
2022-11-08 17:02 ` Anna-Maria Behnsen
2022-11-09 17:13 ` Frederic Weisbecker
2022-11-08 11:48 ` Frederic Weisbecker
2022-11-09 16:39 ` Frederic Weisbecker
2022-11-10 6:34 ` Anna-Maria Behnsen
2022-11-14 13:09 ` Frederic Weisbecker
2022-11-15 11:31 ` Frederic Weisbecker
2022-11-24 7:47 ` Anna-Maria Behnsen
2022-11-28 16:20 ` Frederic Weisbecker
2022-11-29 10:30 ` Frederic Weisbecker [this message]
2022-11-16 13:40 ` Frederic Weisbecker
2022-11-04 14:57 ` [PATCH v4 15/16] timer_migration: Add tracepoints Anna-Maria Behnsen
2022-11-04 14:57 ` [PATCH v4 16/16] timer: Always queue timers on the local CPU Anna-Maria Behnsen
2022-11-08 4:37 ` [PATCH v4 00/16] timer: Move from a push remote at enqueue to a pull at expiry model Pavan Kondeti
2022-11-08 15:06 ` Anna-Maria Behnsen
2022-11-08 16:04 ` Pavan Kondeti
2022-11-08 17:39 ` Anna-Maria Behnsen
2022-11-08 18:48 ` Pavan Kondeti
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