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Message-ID: <CAJZ5v0iM7v6QPKcGNoNqL-PitpOL41byOw_CZGAqhcJkvA1jXA@mail.gmail.com>
Date: Wed, 13 Nov 2019 22:26:36 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Juri Lelli <juri.lelli@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Mel Gorman <mgorman@...e.de>,
Doug Smythies <dsmythies@...us.net>,
Linux PM <linux-pm@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>, sargun@...gun.me,
Tejun Heo <tj@...nel.org>, Xie XiuQi <xiexiuqi@...wei.com>,
xiezhipeng1@...wei.com,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v3] sched/freq: move call to cpufreq_update_util
On Wed, Nov 13, 2019 at 9:21 PM Vincent Guittot
<vincent.guittot@...aro.org> wrote:
>
> update_cfs_rq_load_avg() calls cfs_rq_util_change() everytime pelt decays,
> which might be inefficient when cpufreq driver has rate limitation.
>
> When a task is attached on a CPU, we have call path:
>
> update_load_avg()
> update_cfs_rq_load_avg()
> cfs_rq_util_change -- > trig frequency update
> attach_entity_load_avg()
> cfs_rq_util_change -- > trig frequency update
>
> The 1st frequency update will not take into account the utilization of the
> newly attached task and the 2nd one might be discard because of rate
> limitation of the cpufreq driver.
>
> update_cfs_rq_load_avg() is only called by update_blocked_averages()
> and update_load_avg() so we can move the call to
> cfs_rq_util_change/cpufreq_update_util() into these 2 functions. It's also
> interesting to notice that update_load_avg() already calls directly
> cfs_rq_util_change() for !SMP case.
>
> This changes will also ensure that cpufreq_update_util() is called even
> when there is no more CFS rq in the leaf_cfs_rq_list to update but only
> irq, rt or dl pelt signals.
>
> Reported-by: Doug Smythies <dsmythies@...us.net>
> Fixes: 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load balancing path")
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Looks reasonable to me:
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>
> changes for v3:
> - fix typo
> - test the decay of root cfs_rq even for !CONFIG_FAIR_GROUP_SCHED case
>
> kernel/sched/fair.c | 39 ++++++++++++++++++++++++++-------------
> 1 file changed, 26 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 69a81a5..0a8f4ea 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3504,9 +3504,6 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> cfs_rq->load_last_update_time_copy = sa->last_update_time;
> #endif
>
> - if (decayed)
> - cfs_rq_util_change(cfs_rq, 0);
> -
> return decayed;
> }
>
> @@ -3616,8 +3613,12 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION);
> update_tg_load_avg(cfs_rq, 0);
>
> - } else if (decayed && (flags & UPDATE_TG))
> - update_tg_load_avg(cfs_rq, 0);
> + } else if (decayed) {
> + cfs_rq_util_change(cfs_rq, 0);
> +
> + if (flags & UPDATE_TG)
> + update_tg_load_avg(cfs_rq, 0);
> + }
> }
>
> #ifndef CONFIG_64BIT
> @@ -7543,6 +7544,7 @@ static void update_blocked_averages(int cpu)
> const struct sched_class *curr_class;
> struct rq_flags rf;
> bool done = true;
> + int decayed;
>
> rq_lock_irqsave(rq, &rf);
> update_rq_clock(rq);
> @@ -7552,9 +7554,9 @@ static void update_blocked_averages(int cpu)
> * that RT, DL and IRQ signals have been updated before updating CFS.
> */
> curr_class = rq->curr->sched_class;
> - update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
> - update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
> - update_irq_load_avg(rq, 0);
> + decayed = update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
> + decayed |= update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
> + decayed |= update_irq_load_avg(rq, 0);
>
> /* Don't need periodic decay once load/util_avg are null */
> if (others_have_blocked(rq))
> @@ -7567,9 +7569,13 @@ static void update_blocked_averages(int cpu)
> for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) {
> struct sched_entity *se;
>
> - if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq))
> + if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq)) {
> update_tg_load_avg(cfs_rq, 0);
>
> + if (cfs_rq == &rq->cfs)
> + decayed = 1;
> + }
> +
> /* Propagate pending load changes to the parent, if any: */
> se = cfs_rq->tg->se[cpu];
> if (se && !skip_blocked_update(se))
> @@ -7588,6 +7594,9 @@ static void update_blocked_averages(int cpu)
> }
>
> update_blocked_load_status(rq, !done);
> +
> + if (decayed)
> + cpufreq_update_util(rq, 0);
> rq_unlock_irqrestore(rq, &rf);
> }
>
> @@ -7644,6 +7653,7 @@ static inline void update_blocked_averages(int cpu)
> struct cfs_rq *cfs_rq = &rq->cfs;
> const struct sched_class *curr_class;
> struct rq_flags rf;
> + int decayed;
>
> rq_lock_irqsave(rq, &rf);
> update_rq_clock(rq);
> @@ -7653,13 +7663,16 @@ static inline void update_blocked_averages(int cpu)
> * that RT, DL and IRQ signals have been updated before updating CFS.
> */
> curr_class = rq->curr->sched_class;
> - update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
> - update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
> - update_irq_load_avg(rq, 0);
> + decayed = update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
> + decayed |= update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
> + decayed |= update_irq_load_avg(rq, 0);
>
> - update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq);
> + decayed |= update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq);
>
> update_blocked_load_status(rq, cfs_rq_has_blocked(cfs_rq) || others_have_blocked(rq));
> +
> + if (decayed)
> + cpufreq_update_util(rq, 0);
> rq_unlock_irqrestore(rq, &rf);
> }
>
> --
> 2.7.4
>
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