From: Vincent Guittot <vincent.guittot@linaro.org>
To: Rik van Riel <riel@surriel.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Kernel Team <kernel-team@fb.com>, Paul Turner <pjt@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH 05/15] sched,fair: remove cfs_rqs from leaf_cfs_rq_list bottom up
Date: Wed, 28 Aug 2019 16:09:49 +0200 [thread overview]
Message-ID: <CAKfTPtAoZwmZXthcaP6VQO-0oEOtPfTWwDPtgHfKwBt=+TO2XA@mail.gmail.com> (raw)
In-Reply-To: <20190822021740.15554-6-riel@surriel.com>
On Thu, 22 Aug 2019 at 04:18, Rik van Riel <riel@surriel.com> wrote:
>
> Reducing the overhead of the CPU controller is achieved by not walking
> all the sched_entities every time a task is enqueued or dequeued.
>
> One of the things being checked every single time is whether the cfs_rq
> is on the rq->leaf_cfs_rq_list.
>
> By only removing a cfs_rq from the list once it no longer has children
> on the list, we can avoid walking the sched_entity hierarchy if the bottom
> cfs_rq is on the list, once the runqueues have been flattened.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> kernel/sched/fair.c | 35 ++++++++++++++++++++++++++++++++++-
> 1 file changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a48d0dbfc232..04b216234265 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -369,6 +369,39 @@ static inline void assert_list_leaf_cfs_rq(struct rq *rq)
> SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
> }
>
> +/*
> + * Because list_add_leaf_cfs_rq always places a child cfs_rq on the list
> + * immediately before a parent cfs_rq, and cfs_rqs are removed from the list
> + * bottom-up, we only have to test whether the cfs_rq before us on the list
> + * is our child.
> + */
> +static inline bool child_cfs_rq_on_list(struct cfs_rq *cfs_rq)
> +{
> + struct cfs_rq *prev_cfs_rq;
> + struct list_head *prev;
> +
> + prev = cfs_rq->leaf_cfs_rq_list.prev;
> + prev_cfs_rq = container_of(prev, struct cfs_rq, leaf_cfs_rq_list);
> +
> + return (prev_cfs_rq->tg->parent == cfs_rq->tg);
> +}
> +
> +/*
> + * Remove a cfs_rq from the list if it has no children on the list.
> + * The scheduler iterates over the list regularly; if conditions for
> + * removal are still true, we'll get to this cfs_rq in the future.
> + */
> +static inline void list_del_leaf_cfs_rq_bottom(struct cfs_rq *cfs_rq)
> +{
> + if (!cfs_rq->on_list)
> + return;
> +
> + if (child_cfs_rq_on_list(cfs_rq))
> + return;
> +
> + list_del_leaf_cfs_rq(cfs_rq);
> +}
> +
> /* Iterate thr' all leaf cfs_rq's on a runqueue */
> #define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) \
> list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list, \
> @@ -7723,7 +7756,7 @@ static void update_blocked_averages(int cpu)
> * decayed cfs_rqs linger on the list.
> */
> if (cfs_rq_is_decayed(cfs_rq))
> - list_del_leaf_cfs_rq(cfs_rq);
> + list_del_leaf_cfs_rq_bottom(cfs_rq);
>
> /* Don't need periodic decay once load/util_avg are null */
> if (cfs_rq_has_blocked(cfs_rq))
> --
> 2.20.1
>
next prev parent reply other threads:[~2019-08-28 14:10 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-22 2:17 [PATCH RFC v4 0/15] sched,fair: flatten CPU controller runqueues Rik van Riel
2019-08-22 2:17 ` [PATCH 01/15] sched: introduce task_se_h_load helper Rik van Riel
2019-08-23 18:13 ` Dietmar Eggemann
2019-08-24 0:05 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 02/15] sched: change /proc/sched_debug fields Rik van Riel
2019-08-22 2:17 ` [PATCH 03/15] sched,fair: redefine runnable_load_avg as the sum of task_h_load Rik van Riel
2019-08-28 13:50 ` Vincent Guittot
2019-08-28 14:47 ` Rik van Riel
2019-08-28 15:02 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 04/15] sched,fair: move runnable_load_avg to cfs_rq Rik van Riel
2019-08-22 2:17 ` [PATCH 05/15] sched,fair: remove cfs_rqs from leaf_cfs_rq_list bottom up Rik van Riel
2019-08-28 14:09 ` Vincent Guittot [this message]
2019-08-22 2:17 ` [PATCH 06/15] sched,cfs: use explicit cfs_rq of parent se helper Rik van Riel
2019-08-28 13:53 ` Vincent Guittot
2019-08-28 15:28 ` Rik van Riel
2019-08-28 16:34 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 07/15] sched,cfs: fix zero length timeslice calculation Rik van Riel
2019-08-28 16:59 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 08/15] sched,fair: simplify timeslice length code Rik van Riel
2019-08-28 17:32 ` Vincent Guittot
2019-08-28 23:18 ` Rik van Riel
2019-08-29 14:02 ` Vincent Guittot
2019-08-29 16:00 ` Rik van Riel
2019-08-30 6:41 ` Vincent Guittot
2019-08-30 15:01 ` Rik van Riel
2019-09-02 7:51 ` Vincent Guittot
2019-09-02 17:47 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 09/15] sched,fair: refactor enqueue/dequeue_entity Rik van Riel
2019-09-03 15:38 ` Vincent Guittot
2019-09-03 20:27 ` Rik van Riel
2019-09-04 6:44 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 10/15] sched,fair: add helper functions for flattened runqueue Rik van Riel
2019-08-22 2:17 ` [PATCH 11/15] sched,fair: flatten hierarchical runqueues Rik van Riel
2019-08-23 18:14 ` Dietmar Eggemann
2019-08-24 1:16 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 12/15] sched,fair: flatten update_curr functionality Rik van Riel
2019-08-27 10:37 ` Dietmar Eggemann
2019-08-22 2:17 ` [PATCH 13/15] sched,fair: propagate sum_exec_runtime up the hierarchy Rik van Riel
2019-08-28 7:51 ` Dietmar Eggemann
2019-08-28 13:14 ` Rik van Riel
2019-08-29 17:20 ` Dietmar Eggemann
2019-08-29 18:06 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 14/15] sched,fair: ramp up task_se_h_weight quickly Rik van Riel
2019-08-22 2:17 ` [PATCH 15/15] sched,fair: scale vdiff in wakeup_preempt_entity Rik van Riel
2019-09-02 10:53 ` [PATCH RFC v4 0/15] sched,fair: flatten CPU controller runqueues Dietmar Eggemann
2019-09-03 1:44 ` Rik van Riel
2019-09-06 19:12 [PATCH RFC v5 " Rik van Riel
2019-09-06 19:12 ` [PATCH 05/15] sched,fair: remove cfs_rqs from leaf_cfs_rq_list bottom up Rik van Riel
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