Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 19 Jul 2023 21:29:14 +0800
From:   Aaron Lu <aaron.lu@intel.com>
To:     Vincent Guittot <vincent.guittot@linaro.org>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Daniel Jordan <daniel.m.jordan@oracle.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>,
        Valentin Schneider <vschneid@redhat.com>,
        Tim Chen <tim.c.chen@intel.com>,
        Nitin Tekchandani <nitin.tekchandani@intel.com>,
        Yu Chen <yu.c.chen@intel.com>,
        Waiman Long <longman@redhat.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 3/4] sched/fair: delay update_tg_load_avg() for
 cfs_rq's removed load
Message-ID: <20230719132914.GA91858@ziqianlu-dell>
References: <20230718134120.81199-1-aaron.lu@intel.com>
 <20230718134120.81199-4-aaron.lu@intel.com>
 <CAKfTPtAu33AN6=X82T=yOgm40S8OXi+sPcF0QyD-bYRPV=xPEg@mail.gmail.com>
 <20230719051826.GB84059@ziqianlu-dell>
 <20230719080105.GA90441@ziqianlu-dell>
 <CAKfTPtCnvOehfrz1OSW+rmkKW+28bdGw8fU+AvVrZTxkHibL_g@mail.gmail.com>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <CAKfTPtCnvOehfrz1OSW+rmkKW+28bdGw8fU+AvVrZTxkHibL_g@mail.gmail.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?sjVO/ioq0wwsmvAtKnaEDFs9SKg8Q2d5Gw75eqJIhdAgqmkoeZJTeZhhco+/?=
 =?us-ascii?Q?cg3YUyvi8nwWAk0E0IMOJydHIr5DND2KjAExHMRWftrufcoveGyf5v0MIr1U?=
 =?us-ascii?Q?KAP1KMAk4vudLabUhjZTUTkD5Zr/Q2y+meGxUxTHDhGnauKdjObncbrjUq21?=
 =?us-ascii?Q?jsYqpq4bMVqrkPdH/xYxampXB6eDShOof01fwBqj6wzbPdxbvzcw4TkwfVpf?=
 =?us-ascii?Q?wuvO3OUTdERw8zpsUDaCULYnx3la/RSdr9Cf+fP3tMFktnOUePhy2CkkGIyc?=
 =?us-ascii?Q?vHg1L7X5EzAfjtqBfOldseUj/BE0QXT6Ax6yIXrjSPv8dXu05BSQiXBcRucx?=
 =?us-ascii?Q?5JeByZgGHDWUB0mWc1EcxTFR39WDJN135GQ09b2bzZQFJQQ6m7YHGb+vgN9c?=
 =?us-ascii?Q?X8fjyiRRs1Ur+Vz67m3MtcVZjtwiLdkH2TH1R8WxqoJnTeIVLFAGax4XNvqa?=
 =?us-ascii?Q?BX1UJvple8EhMxC1VKIU24VqvQ1wBi+MpvT7LstxOaImcTOCpu5gD1G7/eYx?=
 =?us-ascii?Q?YEoSlBj+4bTemRA7eSd8ySrVc/Cw7Ui02s4PdLeQvMC9F5ojR+Cw+UjC1ArV?=
 =?us-ascii?Q?cmJY49T8FoTQjSml+2TzAXyZBcueKPWUSjrfOHY+VqaMv/OEQ5P+ETqmuCR+?=
 =?us-ascii?Q?pekh/xi+jtxyMFrdkVTmVsraNqZZ+0eHkdI4YxEXX7f5HbN53fHrMKz3mahk?=
 =?us-ascii?Q?lnLTzJpteHhAPxbP0dDuUfTF/t3LGIzsVX3uoowz5VjYNyKWkChBD+dN8Xds?=
 =?us-ascii?Q?R2FUL70SCW8HnTmYckmJZxFxSf0cj5IsQ8tczSFDjHNom4S1z2fnxi5IKjC6?=
 =?us-ascii?Q?GbDMbbiuCY2X+tiyUG7ZU4kHy9G/9gEepW9Z+51PA2qULibaiFumkNp8ULef?=
 =?us-ascii?Q?F+sE7J2iiCrNbYnb4KHTv77pBWWD6gMkGEXqJFMPmmcHQpiLkIgz5DF4TEKS?=
 =?us-ascii?Q?CskVAdsHsTcXIdnF+pBKWSHfaQytt/BVqrFqNxcZu7HjZWpxGgXDlKIHflrQ?=
 =?us-ascii?Q?MeJbt9VKq0HFT1wNVwlS5xpRqbVBnJDcbaOZal//97ZtMOFGokfc27zrKvvF?=
 =?us-ascii?Q?adB3w5XM0AOdH1LY0ZR9pEdvoh2iWTM1T4TfAGs07T11nl+tA3Zw3mAl8Lds?=
 =?us-ascii?Q?LUJ9Fw/RYOzMKSdENZrIiAcifXdaurzZGakZl+IqlWbZqu1VaO4yHXYcbXLY?=
 =?us-ascii?Q?mAHWKWpy+zCneKAocDeh/q54dMgrvZ+vfFLUZnvbBKJ4pE+TSvwJIt3fAZCJ?=
 =?us-ascii?Q?D36qhcr0r8+ywAaS6eG9bo8dFLvSw1rgx414uiIsaUqZ3KeJWewIbhxZ52Ea?=
 =?us-ascii?Q?dF9i+Ds6lYSN2Aq9YccgXUkcdFE+d0T/FsayGQF1oAirHXywxSoeeGQetIXJ?=
 =?us-ascii?Q?IpCpe+YkqG12iWDIM7acorPYVVlKtjbd1tLxvzSUvzQSSABa3lYyt5K7greY?=
 =?us-ascii?Q?yjrTw8j9ZkcuPtZN7h+LkLM+Nyz0i+hueq0m2iqEsZ+XX3CYS/kovHFRLNik?=
 =?us-ascii?Q?8kvF2bwb2vfX7qXbRVOvnlUW/euIIpozcBwVRhWBtkRyi3M/7D0QyjI1hPFr?=
 =?us-ascii?Q?8/HKu+Od2rYG4Djw1M0VaBJuo+8LCptvQHIidH2D?=
X-MS-Exchange-CrossTenant-Network-Message-Id: fd7194f4-6395-40fd-be5f-08db885c2cd9
X-MS-Exchange-CrossTenant-AuthSource: BL0PR11MB3060.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jul 2023 13:29:27.8155
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 0tKnqH79/fofWlheTO59me2q3FNilaYD9LRubHmx6WWAFQ4QLIjj8Q/HtMPYG/xLqZtgx4I4i6KjfdVKg2hLiw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB5143
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,
        RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,
        SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED
        autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Jul 19, 2023 at 11:47:06AM +0200, Vincent Guittot wrote:
> On Wed, 19 Jul 2023 at 10:01, Aaron Lu <aaron.lu@intel.com> wrote:
> >
> > On Wed, Jul 19, 2023 at 01:18:26PM +0800, Aaron Lu wrote:
> > > Alternatively, I can remove some callsites of update_tg_load_avg() like
> > > you suggested below and only call update_tg_load_avg() when cfs_rq is
> > > decayed(really just decayed, not when it detected it has removed load
> > > pending or load propagated from its children). This way it would give us
> > > similar result as above(roughly once per ms).
> >
> > Something like this: (I think this is better since it removed those
> > unnecessary calls to update_tg_load_avg(), although it is inline but
> > still)
> >
> >
> > From bc749aaefa6bed36aa946921a4006b3dddb69b77 Mon Sep 17 00:00:00 2001
> > From: Aaron Lu <aaron.lu@intel.com>
> > Date: Wed, 19 Jul 2023 13:54:48 +0800
> > Subject: [PATCH] sched/fair: only update_tg_load_avg() when cfs_rq decayed
> >
> > ---
> >  kernel/sched/fair.c | 22 +++++++---------------
> >  1 file changed, 7 insertions(+), 15 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a80a73909dc2..7d5b7352b8b5 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3913,16 +3913,16 @@ static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum
> >  }
> >
> >  /* Update task and its cfs_rq load average */
> > -static inline int propagate_entity_load_avg(struct sched_entity *se)
> > +static inline void propagate_entity_load_avg(struct sched_entity *se)
> >  {
> >         struct cfs_rq *cfs_rq, *gcfs_rq;
> >
> >         if (entity_is_task(se))
> > -               return 0;
> > +               return;
> >
> >         gcfs_rq = group_cfs_rq(se);
> >         if (!gcfs_rq->propagate)
> > -               return 0;
> > +               return;
> >
> >         gcfs_rq->propagate = 0;
> >
> > @@ -3936,8 +3936,6 @@ static inline int propagate_entity_load_avg(struct sched_entity *se)
> >
> >         trace_pelt_cfs_tp(cfs_rq);
> >         trace_pelt_se_tp(se);
> > -
> > -       return 1;
> >  }
> >
> >  /*
> > @@ -3974,9 +3972,8 @@ static inline bool skip_blocked_update(struct sched_entity *se)
> >
> >  static inline void update_tg_load_avg(struct cfs_rq *cfs_rq) {}
> >
> > -static inline int propagate_entity_load_avg(struct sched_entity *se)
> > +static inline void propagate_entity_load_avg(struct sched_entity *se)
> >  {
> > -       return 0;
> >  }
> >
> >  static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum) {}
> > @@ -4086,7 +4083,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> >  {
> >         unsigned long removed_load = 0, removed_util = 0, removed_runnable = 0;
> >         struct sched_avg *sa = &cfs_rq->avg;
> > -       int decayed = 0;
> > +       int decayed;
> >
> >         if (cfs_rq->removed.nr) {
> >                 unsigned long r;
> > @@ -4134,11 +4131,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> >                  */
> >                 add_tg_cfs_propagate(cfs_rq,
> >                         -(long)(removed_runnable * divider) >> SCHED_CAPACITY_SHIFT);
> > -
> > -               decayed = 1;
> >         }
> >
> > -       decayed |= __update_load_avg_cfs_rq(now, cfs_rq);
> > +       decayed = __update_load_avg_cfs_rq(now, cfs_rq);
> >         u64_u32_store_copy(sa->last_update_time,
> >                            cfs_rq->last_update_time_copy,
> >                            sa->last_update_time);
> > @@ -4252,7 +4247,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> >                 __update_load_avg_se(now, cfs_rq, se);
> >
> >         decayed  = update_cfs_rq_load_avg(now, cfs_rq);
> > -       decayed |= propagate_entity_load_avg(se);
> > +       propagate_entity_load_avg(se);
> 
> but then you  also skip the call to cfs_rq_util_change()

Ah right, I missed that, thanks for catching this.

Updated:

From 09a649f8111cfca656b7b735da975ef607b00956 Mon Sep 17 00:00:00 2001
From: Aaron Lu <aaron.lu@intel.com>
Date: Wed, 19 Jul 2023 13:54:48 +0800
Subject: [PATCH] sched/fair: only update_tg_load_avg() when cfs_rq decayed

---
 kernel/sched/fair.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a80a73909dc2..8d4b9e0a19b6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4086,7 +4086,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 {
 	unsigned long removed_load = 0, removed_util = 0, removed_runnable = 0;
 	struct sched_avg *sa = &cfs_rq->avg;
-	int decayed = 0;
+	int decayed;
 
 	if (cfs_rq->removed.nr) {
 		unsigned long r;
@@ -4134,11 +4134,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 		 */
 		add_tg_cfs_propagate(cfs_rq,
 			-(long)(removed_runnable * divider) >> SCHED_CAPACITY_SHIFT);
-
-		decayed = 1;
 	}
 
-	decayed |= __update_load_avg_cfs_rq(now, cfs_rq);
+	decayed = __update_load_avg_cfs_rq(now, cfs_rq);
 	u64_u32_store_copy(sa->last_update_time,
 			   cfs_rq->last_update_time_copy,
 			   sa->last_update_time);
@@ -4242,7 +4240,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
 	u64 now = cfs_rq_clock_pelt(cfs_rq);
-	int decayed;
+	int decayed, propagated;
 
 	/*
 	 * Track task load average for carrying it to new CPU after migrated, and
@@ -4252,7 +4250,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 		__update_load_avg_se(now, cfs_rq, se);
 
 	decayed  = update_cfs_rq_load_avg(now, cfs_rq);
-	decayed |= propagate_entity_load_avg(se);
+	propagated = propagate_entity_load_avg(se);
 
 	if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
 
@@ -4264,19 +4262,16 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 		 * IOW we're enqueueing a task on a new CPU.
 		 */
 		attach_entity_load_avg(cfs_rq, se);
-		update_tg_load_avg(cfs_rq);
-
 	} else if (flags & DO_DETACH) {
 		/*
 		 * DO_DETACH means we're here from dequeue_entity()
 		 * and we are migrating task out of the CPU.
 		 */
 		detach_entity_load_avg(cfs_rq, se);
-		update_tg_load_avg(cfs_rq);
-	} else if (decayed) {
+	} else if (decayed || propagated) {
 		cfs_rq_util_change(cfs_rq, 0);
 
-		if (flags & UPDATE_TG)
+		if (decayed && (flags & UPDATE_TG))
 			update_tg_load_avg(cfs_rq);
 	}
 }
-- 
2.41.0


> >
> >         if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
> >
> > @@ -4264,15 +4259,12 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> >                  * IOW we're enqueueing a task on a new CPU.
> >                  */
> >                 attach_entity_load_avg(cfs_rq, se);
> > -               update_tg_load_avg(cfs_rq);
> > -
> >         } else if (flags & DO_DETACH) {
> >                 /*
> >                  * DO_DETACH means we're here from dequeue_entity()
> >                  * and we are migrating task out of the CPU.
> >                  */
> >                 detach_entity_load_avg(cfs_rq, se);
> > -               update_tg_load_avg(cfs_rq);
> >         } else if (decayed) {
> >                 cfs_rq_util_change(cfs_rq, 0);
> >
> > --
> > 2.41.0
> >