From: Anna-Maria Behnsen <anna-maria@linutronix.de>
To: Frederic Weisbecker <frederic@kernel.org>
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>,
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 v10 18/20] timers: Implement the hierarchical pull model
Date: Mon, 05 Feb 2024 16:59:45 +0100 [thread overview]
Message-ID: <871q9qucjy.fsf@somnus> (raw)
In-Reply-To: <ZbvHvKdpgqfsJp0E@localhost.localdomain>
Frederic Weisbecker <frederic@kernel.org> writes:
> Le Mon, Jan 15, 2024 at 03:37:41PM +0100, Anna-Maria Behnsen a écrit :
>> +static bool tmigr_handle_remote_up(struct tmigr_group *group,
>> + struct tmigr_group *child,
>> + void *ptr)
>> +{
>> + struct tmigr_remote_data *data = ptr;
>> + u64 now, next = KTIME_MAX;
>> + struct tmigr_event *evt;
>> + unsigned long jif;
>> + u8 childmask;
>> +
>> + jif = data->basej;
>> + now = data->now;
>> +
>> + childmask = data->childmask;
>> +
>> +again:
>> + /*
>> + * Handle the group only if @childmask is the migrator or if the
>> + * group has no migrator. Otherwise the group is active and is
>> + * handled by its own migrator.
>> + */
>> + if (!tmigr_check_migrator(group, childmask))
>> + return true;
>> +
>> + raw_spin_lock_irq(&group->lock);
>> +
>> + evt = tmigr_next_expired_groupevt(group, now);
>> +
>> + if (evt) {
>> + unsigned int remote_cpu = evt->cpu;
>> +
>> + raw_spin_unlock_irq(&group->lock);
>> +
>> + next = tmigr_handle_remote_cpu(remote_cpu, now, jif);
>> +
>> + /* check if there is another event, that needs to be handled */
>> + goto again;
>> + } else {
>> + raw_spin_unlock_irq(&group->lock);
>> + }
>> +
>> + /*
>> + * Update of childmask for the next level and keep track of the expiry
>> + * of the first event that needs to be handled
>> + */
>> + data->childmask = group->childmask;
>> + data->firstexp = next;
>
> So assume we have:
>
> [GRP1:0]
> migrator = [GRP0:0]
> active = [GRP0:0]
> nextevt = TIMER3
> / \
> [GRP0:0] [GRP0:1]
> migrator = CPU0 migrator = NONE
> active = CPU0 active = NONE
> nextevt = KTIME_MAX nextevt = TIMER3
> / \ / \
> 0 1 2 3
> idle idle idle idle (TIMER3)
>
> Then CPU 0 goes idle:
>
> [GRP1:0]
> migrator = NONE
> active = NONE
> nextevt = TIMER3
> / \
> [GRP0:0] [GRP0:1]
> migrator = NONE migrator = NONE
> active = NONE active = NONE
> nextevt = KTIME_MAX nextevt = TIMER3
> / \ / \
> 0 1 2 3
> idle idle idle idle (TIMER3)
>
> CPU 0 is the idle migrator and its tmc->wakeup is TIMER3.
> But CPU 0 has a local timer that expires before TIMER3.
>
> When that timer interrupt fires, it raises the softirq, which
> executes on IRQ tail. So CPU0 eventually calls tmigr_handle_remote()
> before TIMER3 has expired.
>
> This leads to tmigr_next_expired_groupevt() to return NULL and then
> data->firstexp = KTIME_MAX and then tmc->wakeup = KTIME_MAX.
>
> Later on, tmigr_new_timer() is called with a KTIME_MAX global
> event and so tmc->wakeup stays with KTIME_MAX, ignoring TIMER3.
>
> It looks like you need to handle the tmigr_next_expired_groupevt()
> case returning NULL.
Yes. You are right. group->next_expiry is updated via
tmigr_next_expired_groupevt(). So I should take this value to rely on
for the firstevt.
But with this, we do not need the return value of
tmigr_handle_remote_cpu(). When the upperst level is inactive and there
is a timer (e.g. propagated there by tmigr_handle_remote_cpu()), the
return value of tmigr_handle_remote_cpu() is the next_expiry of the top
level group. But this value is also noticed by walking the hierarchy up
to the top level with tmigr_handle_remote_up().
Thanks,
Anna-Maria
next prev parent reply other threads:[~2024-02-05 15:59 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-15 14:37 [PATCH v10 00/20] timers: Move from a push remote at enqueue to a pull at expiry model Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 01/20] timers: Restructure get_next_timer_interrupt() Anna-Maria Behnsen
2024-01-17 15:01 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 02/20] timers: Split out get next timer interrupt Anna-Maria Behnsen
2024-01-17 15:06 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 03/20] timers: Move marking timer bases idle into tick_nohz_stop_tick() Anna-Maria Behnsen
2024-01-17 16:02 ` Frederic Weisbecker
2024-01-22 11:45 ` Anna-Maria Behnsen
2024-01-22 21:49 ` Frederic Weisbecker
2024-02-19 8:52 ` [PATCH v10a] " Anna-Maria Behnsen
2024-02-19 22:37 ` Frederic Weisbecker
2024-02-20 10:48 ` Anna-Maria Behnsen
2024-02-20 11:41 ` Frederic Weisbecker
2024-02-20 12:02 ` Anna-Maria Behnsen
2024-02-20 12:34 ` Frederic Weisbecker
2024-02-20 14:00 ` Anna-Maria Behnsen
2024-02-20 15:10 ` Frederic Weisbecker
2024-02-20 15:23 ` Anna-Maria Behnsen
2024-02-20 15:25 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 04/20] timers: Optimization for timer_base_try_to_set_idle() Anna-Maria Behnsen
2024-01-17 16:45 ` Frederic Weisbecker
2024-01-22 11:48 ` Anna-Maria Behnsen
2024-01-22 22:22 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 05/20] timers: Introduce add_timer() variants which modify timer flags Anna-Maria Behnsen
2024-01-17 17:01 ` Frederic Weisbecker
2024-01-22 11:50 ` Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 06/20] workqueue: Use global variant for add_timer() Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 07/20] timers: add_timer_on(): Make sure TIMER_PINNED flag is set Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 08/20] timers: Ease code in run_local_timers() Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 09/20] timers: Split next timer interrupt logic Anna-Maria Behnsen
2024-01-23 14:28 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 10/20] timers: Keep the pinned timers separate from the others Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 11/20] timers: Retrieve next expiry of pinned/non-pinned timers separately Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 12/20] timers: Split out "get next timer interrupt" functionality Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 13/20] timers: Add get next timer interrupt functionality for remote CPUs Anna-Maria Behnsen
2024-02-19 16:04 ` Frederic Weisbecker
2024-02-19 16:57 ` Anna-Maria Behnsen
2024-01-15 14:37 ` [PATCH v10 14/20] timers: Restructure internal locking Anna-Maria Behnsen
2024-01-24 13:56 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 15/20] timers: Check if timers base is handled already Anna-Maria Behnsen
2024-01-24 14:22 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 16/20] tick/sched: Split out jiffies update helper function Anna-Maria Behnsen
2024-01-24 14:42 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 17/20] timers: Introduce function to check timer base is_idle flag Anna-Maria Behnsen
2024-01-24 14:52 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 18/20] timers: Implement the hierarchical pull model Anna-Maria Behnsen
2024-01-25 14:30 ` Frederic Weisbecker
2024-01-28 15:58 ` Anna-Maria Behnsen
2024-01-30 15:29 ` Frederic Weisbecker
2024-01-30 16:45 ` Anna-Maria Behnsen
2024-01-26 12:53 ` Frederic Weisbecker
2024-01-27 22:54 ` Frederic Weisbecker
2024-01-29 10:50 ` Anna-Maria Behnsen
2024-01-29 22:21 ` Frederic Weisbecker
2024-01-30 13:32 ` Anna-Maria Behnsen
2024-01-29 13:50 ` Paul E. McKenney
2024-01-29 1:04 ` Frederic Weisbecker
2024-01-30 17:56 ` Anna-Maria Behnsen
2024-01-30 21:13 ` Frederic Weisbecker
2024-01-31 11:19 ` Anna-Maria Behnsen
2024-01-30 15:37 ` Frederic Weisbecker
2024-02-01 14:59 ` Anna-Maria Behnsen
2024-02-01 15:05 ` Frederic Weisbecker
2024-02-01 16:15 ` Anna-Maria Behnsen
2024-02-01 17:43 ` Frederic Weisbecker
2024-02-01 20:52 ` Anna-Maria Behnsen
2024-02-05 13:29 ` Anna-Maria Behnsen
2024-02-05 20:30 ` Frederic Weisbecker
2024-02-06 10:06 ` Anna-Maria Behnsen
2024-02-06 10:29 ` Frederic Weisbecker
2024-02-01 16:33 ` Frederic Weisbecker
2024-02-05 15:59 ` Anna-Maria Behnsen [this message]
2024-02-05 20:28 ` Frederic Weisbecker
2024-02-04 22:02 ` Frederic Weisbecker
2024-02-06 11:03 ` Anna-Maria Behnsen
2024-02-06 11:11 ` Frederic Weisbecker
2024-02-04 22:32 ` Frederic Weisbecker
2024-02-06 11:36 ` Anna-Maria Behnsen
2024-02-06 13:21 ` Frederic Weisbecker
2024-02-06 14:13 ` Anna-Maria Behnsen
2024-02-06 14:21 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 19/20] timer_migration: Add tracepoints Anna-Maria Behnsen
2024-02-01 16:47 ` Frederic Weisbecker
2024-01-15 14:37 ` [PATCH v10 20/20] timers: Always queue timers on the local CPU Anna-Maria Behnsen
2024-02-01 17:36 ` Frederic Weisbecker
2024-02-01 20:58 ` Anna-Maria Behnsen
2024-02-02 11:57 ` Frederic Weisbecker
2024-01-30 22:07 ` [PATCH v10 00/20] timers: Move from a push remote at enqueue to a pull at expiry model Christian Loehle
2024-02-01 15:03 ` Anna-Maria Behnsen
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