From: Vincent Guittot <vincent.guittot@linaro.org>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Phil Auld <pauld@redhat.com>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Odin Ugedal <odin@uged.al>, Rik van Riel <riel@surriel.com>,
Giovanni Gherdovich <ggherdovich@suse.cz>
Subject: Re: [RFC PATCH v2 5/5] sched/fair: Simplify ancestor enqueue loops
Date: Thu, 9 Sep 2021 16:04:02 +0200 [thread overview]
Message-ID: <CAKfTPtDwOGu9kkMdXDx=+mGVGq_EmF0wgLen7hYO+VEy+j6rig@mail.gmail.com> (raw)
In-Reply-To: <20210819175034.4577-6-mkoutny@suse.com>
On Thu, 19 Aug 2021 at 19:50, Michal Koutný <mkoutny@suse.com> wrote:
>
> When a task is enqueued or cfs_rq is unthrottled we have work to do from
> the cfs_rq in question possibly up to root. The important nodes on the
> path are throttled cfs_rqs or cfs_rqs already enqueud to their parent.
>
> Instead of multiple (interrupted) loops make all work in a single loop
> and decide what all needs to be done inside it. This undoes parts of
These multiple break loops have been done to make unthrottle_cfs_rq,
throttle_cfs_rq, enqueue_task_fair and dequeue_task_fair to follow the
same pattern and I don't see any good reason to break this
> commit 39f23ce07b93 ("sched/fair: Fix unthrottle_cfs_rq() for
> leaf_cfs_rq list") but it should not bring any functional changes.
>
> Note some PELT stats update code is duplicated both in enqueue_entity
> and the ancestor loop (update_load_avg, se_update_runnable,
> update_cfs_group). It'd be nice to factor these out, however, the later
> parts of enqueue_entity rely on the updates, so stick with the current
> repetition.
>
> Signed-off-by: Michal Koutný <mkoutny@suse.com>
> ---
> kernel/sched/fair.c | 57 +++++++++++++++++----------------------------
> 1 file changed, 21 insertions(+), 36 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 9978485334ec..79f183336fa8 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4883,6 +4883,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
> struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
> struct sched_entity *se;
> long task_delta, idle_task_delta;
> + int enqueue = 1;
>
> cfs_rq->throttled = 0;
>
> @@ -4911,29 +4912,21 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
> task_delta = cfs_rq->h_nr_running;
> idle_task_delta = cfs_rq->idle_h_nr_running;
> for_each_sched_entity(se) {
> - if (se->on_rq)
> - break;
> cfs_rq = cfs_rq_of(se);
> - enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
> -
> - cfs_rq->h_nr_running += task_delta;
> - cfs_rq->idle_h_nr_running += idle_task_delta;
>
> - /* end evaluation on encountering a throttled cfs_rq */
> - if (cfs_rq_throttled(cfs_rq))
> - goto unthrottle_throttle;
> - }
> -
> - for_each_sched_entity(se) {
> - cfs_rq = cfs_rq_of(se);
> -
> - update_load_avg(cfs_rq, se, UPDATE_TG);
> - se_update_runnable(se);
> + if (se->on_rq)
> + enqueue = 0;
> + if (enqueue)
> + enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
> + else {
> + update_load_avg(cfs_rq, se, UPDATE_TG);
> + se_update_runnable(se);
> + /* XXX: no update_cfs_group(se); */
> + }
>
> cfs_rq->h_nr_running += task_delta;
> cfs_rq->idle_h_nr_running += idle_task_delta;
>
> -
> /* end evaluation on encountering a throttled cfs_rq */
> if (cfs_rq_throttled(cfs_rq))
> goto unthrottle_throttle;
> @@ -5537,6 +5530,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> struct sched_entity *se = &p->se;
> int idle_h_nr_running = task_has_idle_policy(p);
> int task_new = !(flags & ENQUEUE_WAKEUP);
> + int enqueue = 1;
>
> /*
> * The code below (indirectly) updates schedutil which looks at
> @@ -5555,27 +5549,18 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
>
> for_each_sched_entity(se) {
> - if (se->on_rq)
> - break;
> cfs_rq = cfs_rq_of(se);
> - enqueue_entity(cfs_rq, se, flags);
>
> - cfs_rq->h_nr_running++;
> - cfs_rq->idle_h_nr_running += idle_h_nr_running;
> -
> - /* end evaluation on encountering a throttled cfs_rq */
> - if (cfs_rq_throttled(cfs_rq))
> - goto enqueue_throttle;
> -
> - flags = ENQUEUE_WAKEUP;
> - }
> -
> - for_each_sched_entity(se) {
> - cfs_rq = cfs_rq_of(se);
> -
> - update_load_avg(cfs_rq, se, UPDATE_TG);
> - se_update_runnable(se);
> - update_cfs_group(se);
> + if (se->on_rq)
> + enqueue = 0;
> + if (enqueue) {
> + enqueue_entity(cfs_rq, se, flags);
> + flags = ENQUEUE_WAKEUP;
> + } else {
> + update_load_avg(cfs_rq, se, UPDATE_TG);
> + se_update_runnable(se);
> + update_cfs_group(se);
> + }
>
> cfs_rq->h_nr_running++;
> cfs_rq->idle_h_nr_running += idle_h_nr_running;
> --
> 2.32.0
>
next prev parent reply other threads:[~2021-09-09 14:40 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-19 17:50 [RFC PATCH v2 0/5] leaf_cfs_rq_list cleanups and fix Michal Koutný
2021-08-19 17:50 ` [RFC PATCH v2 1/5] sched/fair: Add ancestors of unthrottled undecayed cfs_rq Michal Koutný
2021-09-09 13:57 ` Vincent Guittot
2021-09-10 11:35 ` Michal Koutný
2021-09-10 13:17 ` Vincent Guittot
2021-08-19 17:50 ` [RFC PATCH v2 2/5] sched: Add group_se() helper Michal Koutný
2021-08-19 17:50 ` [RFC PATCH v2 3/5] sched/fair: Rename leaf_list to more fitting load_list Michal Koutný
2021-09-21 19:06 ` Odin Ugedal
2021-08-19 17:50 ` [RFC PATCH v2 4/5] sched/fair: Simplify load_cfs_rq_list maintenance Michal Koutný
2021-09-10 14:19 ` Vincent Guittot
2021-09-14 9:22 ` Michal Koutný
2021-09-14 9:45 ` Vincent Guittot
2021-09-15 12:30 ` Vincent Guittot
2021-09-15 18:59 ` Odin Ugedal
2021-09-21 19:21 ` Odin Ugedal
2021-09-21 21:40 ` Michal Koutný
2021-08-19 17:50 ` [RFC PATCH v2 5/5] sched/fair: Simplify ancestor enqueue loops Michal Koutný
2021-09-09 14:04 ` Vincent Guittot [this message]
2021-09-10 11:35 ` Michal Koutný
2021-09-10 11:43 ` Vincent Guittot
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