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>,
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: Sun, 4 Feb 2024 23:32:07 +0100 [thread overview]
Message-ID: <ZcAQZ8-gbEYaQflu@pavilion.home> (raw)
In-Reply-To: <20240115143743.27827-19-anna-maria@linutronix.de>
Le Mon, Jan 15, 2024 at 03:37:41PM +0100, Anna-Maria Behnsen a écrit :
> +/*
> + * Returns true, if there is nothing to be propagated to the next level
> + *
> + * @data->firstexp is set to expiry of first gobal event of the (top level of
> + * the) hierarchy, but only when hierarchy is completely idle.
> + *
> + * This is the only place where the group event expiry value is set.
> + */
> +static
> +bool tmigr_update_events(struct tmigr_group *group, struct tmigr_group *child,
> + struct tmigr_walk *data, union tmigr_state childstate,
> + union tmigr_state groupstate)
> +{
> + struct tmigr_event *evt, *first_childevt;
> + bool walk_done, remote = data->remote;
> + bool leftmost_change = false;
> + u64 nextexp;
> +
> + if (child) {
> + raw_spin_lock(&child->lock);
> + raw_spin_lock_nested(&group->lock, SINGLE_DEPTH_NESTING);
> +
> + if (childstate.active) {
> + walk_done = true;
> + goto unlock;
> + }
> +
> + first_childevt = tmigr_next_groupevt(child);
> + nextexp = child->next_expiry;
> + evt = &child->groupevt;
> + } else {
> + nextexp = data->nextexp;
> +
> + first_childevt = evt = data->evt;
> +
> + /*
> + * Walking the hierarchy is required in any case when a
> + * remote expiry was done before. This ensures to not lose
> + * already queued events in non active groups (see section
> + * "Required event and timerqueue update after a remote
> + * expiry" in the documentation at the top).
> + *
> + * The two call sites which are executed without a remote expiry
> + * before, are not prevented from propagating changes through
> + * the hierarchy by the return:
> + * - When entering this path by tmigr_new_timer(), @evt->ignore
> + * is never set.
> + * - tmigr_inactive_up() takes care of the propagation by
> + * itself and ignores the return value. But an immediate
> + * return is required because nothing has to be done in this
> + * level as the event could be ignored.
> + */
> + if (evt->ignore && !remote)
> + return true;
> +
> + raw_spin_lock(&group->lock);
> + }
> +
> + if (nextexp == KTIME_MAX) {
> + evt->ignore = true;
> +
> + /*
> + * When the next child event could be ignored (nextexp is
> + * KTIME_MAX) and there was no remote timer handling before or
> + * the group is already active, there is no need to walk the
> + * hierarchy even if there is a parent group.
> + *
> + * The other way round: even if the event could be ignored, but
> + * if a remote timer handling was executed before and the group
> + * is not active, walking the hierarchy is required to not miss
> + * an enqueued timer in the non active group. The enqueued timer
> + * of the group needs to be propagated to a higher level to
> + * ensure it is handled.
> + */
> + if (!remote || groupstate.active) {
> + walk_done = true;
> + goto unlock;
So if the current tmc going inactive was the migrator for the whole hierarchy
and it is reaching here the top-level, this assumes that if none of this tmc's
groups have a timer, then it can just return. But what if the top level has
timers from other children? Who is going to handle them then?
Should this be "goto check_toplvl" instead?
Thanks.
> + }
> + } else {
> + /*
> + * An update of @evt->cpu and @evt->ignore flag is required only
> + * when @child is set (the child is equal or higher than lvl0),
> + * but it doesn't matter if it is written once more to the per
> + * CPU event; make the update unconditional.
> + */
> + evt->cpu = first_childevt->cpu;
> + evt->ignore = false;
> + }
> +
> + walk_done = !group->parent;
> +
> + /*
> + * If the child event is already queued in the group, remove it from the
> + * queue when the expiry time changed only.
> + */
> + if (timerqueue_node_queued(&evt->nextevt)) {
> + if (evt->nextevt.expires == nextexp)
> + goto check_toplvl;
> +
> + leftmost_change = timerqueue_getnext(&group->events) == &evt->nextevt;
> + if (!timerqueue_del(&group->events, &evt->nextevt))
> + WRITE_ONCE(group->next_expiry, KTIME_MAX);
> + }
> +
> + evt->nextevt.expires = nextexp;
> +
> + if (timerqueue_add(&group->events, &evt->nextevt)) {
> + leftmost_change = true;
> + WRITE_ONCE(group->next_expiry, nextexp);
> + }
> +
> +check_toplvl:
> + if (walk_done && (groupstate.migrator == TMIGR_NONE)) {
> + /*
> + * Nothing to do when first event didn't changed and update was
> + * done during remote timer handling.
> + */
> + if (remote && !leftmost_change)
> + goto unlock;
> + /*
> + * The top level group is idle and it has to be ensured the
> + * global timers are handled in time. (This could be optimized
> + * by keeping track of the last global scheduled event and only
> + * arming it on the CPU if the new event is earlier. Not sure if
> + * its worth the complexity.)
> + */
> + data->firstexp = tmigr_next_groupevt_expires(group);
> + }
> +
> +unlock:
> + raw_spin_unlock(&group->lock);
> +
> + if (child)
> + raw_spin_unlock(&child->lock);
> +
> + return walk_done;
> +}
next prev parent reply other threads:[~2024-02-04 22:32 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
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 [this message]
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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