From nobody Sun May 10 15:45:29 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0D8EC433F5 for ; Fri, 29 Apr 2022 14:13:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376793AbiD2OQ2 (ORCPT ); Fri, 29 Apr 2022 10:16:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47416 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1357181AbiD2OQX (ORCPT ); Fri, 29 Apr 2022 10:16:23 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id D23561A836 for ; Fri, 29 Apr 2022 07:13:04 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9BD6B106F; Fri, 29 Apr 2022 07:13:04 -0700 (PDT) Received: from localhost.localdomain (FVFF7649Q05P.cambridge.arm.com [10.1.32.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 423503F774; Fri, 29 Apr 2022 07:13:03 -0700 (PDT) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, qperret@google.com, tao.zhou@linux.dev, Vincent Donnefort Subject: [PATCH v8 1/7] sched/fair: Provide u64 read for 32-bits arch helper Date: Fri, 29 Apr 2022 15:11:42 +0100 Message-Id: <20220429141148.181816-2-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220429141148.181816-1-vincent.donnefort@arm.com> References: <20220429141148.181816-1-vincent.donnefort@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Introducing macro helpers u64_u32_{store,load}() to factorize lockless accesses to u64 variables for 32-bits architectures. Users are for now cfs_rq.min_vruntime and sched_avg.last_update_time. To accommodate the later where the copy lies outside of the structure (cfs_rq.last_udpate_time_copy instead of sched_avg.last_update_time_copy), use the _copy() version of those helpers. Those new helpers encapsulate smp_rmb() and smp_wmb() synchronization and therefore, have a small penalty in set_task_rq_fair() and init_cfs_rq(). Signed-off-by: Vincent Donnefort diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 4c420124b5d6..abd1feeec0c2 100644 Reviewed-by: Dietmar Eggemann --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -600,11 +600,8 @@ static void update_min_vruntime(struct cfs_rq *cfs_rq) } =20 /* ensure we never gain time by being placed backwards. */ - cfs_rq->min_vruntime =3D max_vruntime(cfs_rq->min_vruntime, vruntime); -#ifndef CONFIG_64BIT - smp_wmb(); - cfs_rq->min_vruntime_copy =3D cfs_rq->min_vruntime; -#endif + u64_u32_store(cfs_rq->min_vruntime, + max_vruntime(cfs_rq->min_vruntime, vruntime)); } =20 static inline bool __entity_less(struct rb_node *a, const struct rb_node *= b) @@ -3301,6 +3298,11 @@ static inline void cfs_rq_util_change(struct cfs_rq = *cfs_rq, int flags) } =20 #ifdef CONFIG_SMP +static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) +{ + return u64_u32_load_copy(cfs_rq->avg.last_update_time, + cfs_rq->last_update_time_copy); +} #ifdef CONFIG_FAIR_GROUP_SCHED /* * Because list_add_leaf_cfs_rq always places a child cfs_rq on the list @@ -3411,27 +3413,9 @@ void set_task_rq_fair(struct sched_entity *se, if (!(se->avg.last_update_time && prev)) return; =20 -#ifndef CONFIG_64BIT - { - u64 p_last_update_time_copy; - u64 n_last_update_time_copy; - - do { - p_last_update_time_copy =3D prev->load_last_update_time_copy; - n_last_update_time_copy =3D next->load_last_update_time_copy; - - smp_rmb(); + p_last_update_time =3D cfs_rq_last_update_time(prev); + n_last_update_time =3D cfs_rq_last_update_time(next); =20 - p_last_update_time =3D prev->avg.last_update_time; - n_last_update_time =3D next->avg.last_update_time; - - } while (p_last_update_time !=3D p_last_update_time_copy || - n_last_update_time !=3D n_last_update_time_copy); - } -#else - p_last_update_time =3D prev->avg.last_update_time; - n_last_update_time =3D next->avg.last_update_time; -#endif __update_load_avg_blocked_se(p_last_update_time, se); se->avg.last_update_time =3D n_last_update_time; } @@ -3786,8 +3770,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) decayed |=3D __update_load_avg_cfs_rq(now, cfs_rq); =20 #ifndef CONFIG_64BIT - smp_wmb(); - cfs_rq->load_last_update_time_copy =3D sa->last_update_time; + u64_u32_store_copy(sa->last_update_time, + cfs_rq->last_update_time_copy, + sa->last_update_time); #endif =20 return decayed; @@ -3921,27 +3906,6 @@ static inline void update_load_avg(struct cfs_rq *cf= s_rq, struct sched_entity *s } } =20 -#ifndef CONFIG_64BIT -static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) -{ - u64 last_update_time_copy; - u64 last_update_time; - - do { - last_update_time_copy =3D cfs_rq->load_last_update_time_copy; - smp_rmb(); - last_update_time =3D cfs_rq->avg.last_update_time; - } while (last_update_time !=3D last_update_time_copy); - - return last_update_time; -} -#else -static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) -{ - return cfs_rq->avg.last_update_time; -} -#endif - /* * Synchronize entity load avg of dequeued entity without locking * the previous rq. @@ -6991,21 +6955,8 @@ static void migrate_task_rq_fair(struct task_struct = *p, int new_cpu) if (READ_ONCE(p->__state) =3D=3D TASK_WAKING) { struct sched_entity *se =3D &p->se; struct cfs_rq *cfs_rq =3D cfs_rq_of(se); - u64 min_vruntime; =20 -#ifndef CONFIG_64BIT - u64 min_vruntime_copy; - - do { - min_vruntime_copy =3D cfs_rq->min_vruntime_copy; - smp_rmb(); - min_vruntime =3D cfs_rq->min_vruntime; - } while (min_vruntime !=3D min_vruntime_copy); -#else - min_vruntime =3D cfs_rq->min_vruntime; -#endif - - se->vruntime -=3D min_vruntime; + se->vruntime -=3D u64_u32_load(cfs_rq->min_vruntime); } =20 if (p->on_rq =3D=3D TASK_ON_RQ_MIGRATING) { @@ -11453,10 +11404,7 @@ static void set_next_task_fair(struct rq *rq, stru= ct task_struct *p, bool first) void init_cfs_rq(struct cfs_rq *cfs_rq) { cfs_rq->tasks_timeline =3D RB_ROOT_CACHED; - cfs_rq->min_vruntime =3D (u64)(-(1LL << 20)); -#ifndef CONFIG_64BIT - cfs_rq->min_vruntime_copy =3D cfs_rq->min_vruntime; -#endif + u64_u32_store(cfs_rq->min_vruntime, (u64)(-(1LL << 20))); #ifdef CONFIG_SMP raw_spin_lock_init(&cfs_rq->removed.lock); #endif diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 762be73972bd..e2cf6e48b165 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -513,6 +513,45 @@ struct cfs_bandwidth { }; =20 #endif /* CONFIG_CGROUP_SCHED */ =20 +/* + * u64_u32_load/u64_u32_store + * + * Use a copy of a u64 value to protect against data race. This is only + * applicable for 32-bits architectures. + */ +#ifdef CONFIG_64BIT +# define u64_u32_load_copy(var, copy) var +# define u64_u32_store_copy(var, copy, val) (var =3D val) +#else +# define u64_u32_load_copy(var, copy) \ +({ \ + u64 __val, __val_copy; \ + do { \ + __val_copy =3D copy; \ + /* \ + * paired with u64_u32_store, ordering access \ + * to var and copy. \ + */ \ + smp_rmb(); \ + __val =3D var; \ + } while (__val !=3D __val_copy); \ + __val; \ +}) +# define u64_u32_store_copy(var, copy, val) \ +do { \ + typeof(val) __val =3D (val); \ + var =3D __val; \ + /* \ + * paired with u64_u32_load, ordering access to var and \ + * copy. \ + */ \ + smp_wmb(); \ + copy =3D __val; \ +} while (0) +#endif +# define u64_u32_load(var) u64_u32_load_copy(var, var##_copy) +# define u64_u32_store(var, val) u64_u32_store_copy(var, var##_copy, val) + /* CFS-related fields in a runqueue */ struct cfs_rq { struct load_weight load; @@ -553,7 +592,7 @@ struct cfs_rq { */ struct sched_avg avg; #ifndef CONFIG_64BIT - u64 load_last_update_time_copy; + u64 last_update_time_copy; #endif struct { raw_spinlock_t lock ____cacheline_aligned; --=20 2.25.1 From nobody Sun May 10 15:45:29 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7775C433EF for ; Fri, 29 Apr 2022 14:13:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376640AbiD2OQe (ORCPT ); Fri, 29 Apr 2022 10:16:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47432 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1357581AbiD2OQZ (ORCPT ); Fri, 29 Apr 2022 10:16:25 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 5BFF820F62 for ; Fri, 29 Apr 2022 07:13:06 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2B29111FB; Fri, 29 Apr 2022 07:13:06 -0700 (PDT) Received: from localhost.localdomain (FVFF7649Q05P.cambridge.arm.com [10.1.32.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id CC5693F774; Fri, 29 Apr 2022 07:13:04 -0700 (PDT) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, qperret@google.com, tao.zhou@linux.dev, Vincent Donnefort Subject: [PATCH v8 2/7] sched/fair: Decay task PELT values during wakeup migration Date: Fri, 29 Apr 2022 15:11:43 +0100 Message-Id: <20220429141148.181816-3-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220429141148.181816-1-vincent.donnefort@arm.com> References: <20220429141148.181816-1-vincent.donnefort@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Before being migrated to a new CPU, a task sees its PELT values synchronized with rq last_update_time. Once done, that same task will also have its sched_avg last_update_time reset. This means the time between the migration and the last clock update will not be accounted for in util_avg and a discontinuity will appear. This issue is amplified by the PELT clock scaling. It takes currently one tick after the CPU being idle to let clock_pelt catching up clock_task. This is especially problematic for asymmetric CPU capacity systems which need stable util_avg signals for task placement and energy estimation. Ideally, this problem would be solved by updating the runqueue clocks before the migration. But that would require taking the runqueue lock which is quite expensive [1]. Instead estimate the missing time and update the task util_avg with that value. To that end, we need sched_clock_cpu() but it is a costly function. Limit the usage to the case where the source CPU is idle as we know this is when the clock is having the biggest risk of being outdated. In this such case, let's call it cfs_idle_lag the delta time between the rq_clock_pelt value at rq idle and cfs_rq idle. And rq_idle_lag the delta between "now" and the rq_clock_pelt at rq idle. The estimated PELT clock is then: last_update_time + (the cfs_rq's last_update_time) cfs_idle_lag + (delta between cfs_rq's update and rq's update) rq_idle_lag (delta between rq's update and now) last_update_time =3D cfs_rq_clock_pelt() =3D rq_clock_pelt() - cfs->throttled_clock_pelt_time cfs_idle_lag =3D rq_clock_pelt()@rq_idle - rq_clock_pelt()@cfs_rq_idle rq_idle_lag =3D sched_clock_cpu() - rq_clock()@rq_idle The rq_clock_pelt() from last_update_time being the same as rq_clock_pelt()@cfs_rq_idle, we can write: estimation =3D rq_clock_pelt()@rq_idle - cfs->throttled_clock_pelt_time + sched_clock_cpu() - rq_clock()@rq_idle The clocks being not accessible without the rq lock taken, some timestamps are created: rq_clock_pelt()@rq_idle is rq->clock_pelt_idle rq_clock()@rq_idle is rq->enter_idle cfs->throttled_clock_pelt_time is cfs_rq->throttled_pelt_idle The rq_idle_lqg part of the missing time is however an estimation that doesn't take into account IRQ and Paravirt time. [1] https://lore.kernel.org/all/20190709115759.10451-1-chris.redpath@arm.co= m/ Signed-off-by: Vincent Donnefort diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index abd1feeec0c2..4e9e0d453a00 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3330,21 +3330,15 @@ static inline bool child_cfs_rq_on_list(struct cfs_= rq *cfs_rq) return (prev_cfs_rq->tg->parent =3D=3D cfs_rq->tg); } =20 -static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) +static inline bool load_avg_is_decayed(struct sched_avg *sa) { - if (cfs_rq->load.weight) - return false; - - if (cfs_rq->avg.load_sum) + if (sa->load_sum) return false; =20 - if (cfs_rq->avg.util_sum) + if (sa->util_sum) return false; =20 - if (cfs_rq->avg.runnable_sum) - return false; - - if (child_cfs_rq_on_list(cfs_rq)) + if (sa->runnable_sum) return false; =20 /* @@ -3352,9 +3346,23 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *= cfs_rq) * Make sure that rounding and/or propagation of PELT values never * break this. */ - SCHED_WARN_ON(cfs_rq->avg.load_avg || - cfs_rq->avg.util_avg || - cfs_rq->avg.runnable_avg); + SCHED_WARN_ON(sa->load_avg || + sa->util_avg || + sa->runnable_avg); + + return true; +} + +static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) +{ + if (cfs_rq->load.weight) + return false; + + if (!load_avg_is_decayed(&cfs_rq->avg)) + return false; + + if (child_cfs_rq_on_list(cfs_rq)) + return false; =20 return true; } @@ -3694,6 +3702,79 @@ static inline void add_tg_cfs_propagate(struct cfs_r= q *cfs_rq, long runnable_sum =20 #endif /* CONFIG_FAIR_GROUP_SCHED */ =20 +#ifdef CONFIG_NO_HZ_COMMON +static inline void migrate_se_pelt_lag(struct sched_entity *se) +{ + u64 throttled =3D 0, now; + struct cfs_rq *cfs_rq; + struct rq *rq; + bool is_idle; + + if (load_avg_is_decayed(&se->avg)) + return; + + cfs_rq =3D cfs_rq_of(se); + rq =3D rq_of(cfs_rq); + + rcu_read_lock(); + is_idle =3D is_idle_task(rcu_dereference(rq->curr)); + rcu_read_unlock(); + + /* + * The lag estimation comes with a cost we don't want to pay all the + * time. Hence, limiting to the case where the source CPU is idle and + * we know we are at the greatest risk to have an outdated clock. + */ + if (!is_idle) + return; + + /* + * estimated "now" is: + * last_update_time + (the cfs_rq's last_update_time) + * cfs_idle_lag + (delta between cfs_rq's update and rq's update) + * rq_idle_lag (delta between rq's update and now) + * + * last_update_time =3D cfs_rq_clock_pelt() + * =3D rq_clock_pelt() - cfs->throttled_clock_pelt_time + * + * cfs_idle_lag =3D rq_clock_pelt()@rq_idle - + * rq_clock_pelt()@cfs_rq_idle + * + * rq_idle_lag =3D sched_clock_cpu() - rq_clock()@rq_idle + * + * The rq_clock_pelt() from last_update_time being the same as + * rq_clock_pelt()@cfs_rq_idle, we can write: + * + * now =3D rq_clock_pelt()@rq_idle - cfs->throttled_clock_pelt_time + + * sched_clock_cpu() - rq_clock()@rq_idle + * + * Where: + * rq_clock_pelt()@rq_idle is rq->clock_pelt_idle + * rq_clock()@rq_idle is rq->enter_idle + * cfs->throttled_clock_pelt_time is cfs_rq->throttled_pelt_idle + */ + +#ifdef CONFIG_CFS_BANDWIDTH + throttled =3D u64_u32_load(cfs_rq->throttled_pelt_idle); + /* The clock has been stopped for throttling */ + if (throttled =3D=3D U64_MAX) + return; +#endif + now =3D u64_u32_load(rq->clock_pelt_idle); + now -=3D throttled; + + /* An update happened while computing lag */ + if (now < cfs_rq_last_update_time(cfs_rq)) + return; + + now +=3D sched_clock_cpu(cpu_of(rq)) - u64_u32_load(rq->enter_idle); + + __update_load_avg_blocked_se(now, se); +} +#else +static void migrate_se_pelt_lag(struct sched_entity *se) {} +#endif + /** * update_cfs_rq_load_avg - update the cfs_rq's load/util averages * @now: current time, as per cfs_rq_clock_pelt() @@ -4429,6 +4510,9 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_en= tity *se, int flags) */ if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) !=3D DEQUEUE_SAVE) update_min_vruntime(cfs_rq); + + if (cfs_rq->nr_running =3D=3D 0) + update_idle_cfs_rq_clock_pelt(cfs_rq); } =20 /* @@ -6946,6 +7030,8 @@ static void detach_entity_cfs_rq(struct sched_entity = *se); */ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) { + struct sched_entity *se =3D &p->se; + /* * As blocked tasks retain absolute vruntime the migration needs to * deal with this by subtracting the old and adding the new @@ -6953,7 +7039,6 @@ static void migrate_task_rq_fair(struct task_struct *= p, int new_cpu) * the task on the new runqueue. */ if (READ_ONCE(p->__state) =3D=3D TASK_WAKING) { - struct sched_entity *se =3D &p->se; struct cfs_rq *cfs_rq =3D cfs_rq_of(se); =20 se->vruntime -=3D u64_u32_load(cfs_rq->min_vruntime); @@ -6965,25 +7050,29 @@ static void migrate_task_rq_fair(struct task_struct= *p, int new_cpu) * rq->lock and can modify state directly. */ lockdep_assert_rq_held(task_rq(p)); - detach_entity_cfs_rq(&p->se); + detach_entity_cfs_rq(se); =20 } else { + remove_entity_load_avg(se); + /* - * We are supposed to update the task to "current" time, then - * its up to date and ready to go to new CPU/cfs_rq. But we - * have difficulty in getting what current time is, so simply - * throw away the out-of-date time. This will result in the - * wakee task is less decayed, but giving the wakee more load - * sounds not bad. + * Here, the task's PELT values have been updated according to + * the current rq's clock. But if that clock hasn't been + * updated in a while, a substantial idle time will be missed, + * leading to an inflation after wake-up on the new rq. + * + * Estimate the missing time from the cfs_rq last_update_time + * and update sched_avg to improve the PELT continuity after + * migration. */ - remove_entity_load_avg(&p->se); + migrate_se_pelt_lag(se); } =20 /* Tell new CPU we are migrated */ - p->se.avg.last_update_time =3D 0; + se->avg.last_update_time =3D 0; =20 /* We have migrated, no longer consider this task hot */ - p->se.exec_start =3D 0; + se->exec_start =3D 0; =20 update_scan_period(p, new_cpu); } @@ -8149,6 +8238,10 @@ static bool __update_blocked_fair(struct rq *rq, boo= l *done) if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq)) { update_tg_load_avg(cfs_rq); =20 + /* sync clock_pelt_idle with last update */ + if (cfs_rq->nr_running =3D=3D 0) + update_idle_cfs_rq_clock_pelt(cfs_rq); + if (cfs_rq =3D=3D &rq->cfs) decayed =3D true; } diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h index 4ff2ed4f8fa1..9aed92262bd9 100644 --- a/kernel/sched/pelt.h +++ b/kernel/sched/pelt.h @@ -61,6 +61,23 @@ static inline void cfs_se_util_change(struct sched_avg *= avg) WRITE_ONCE(avg->util_est.enqueued, enqueued); } =20 +static inline u64 rq_clock_pelt(struct rq *rq) +{ + lockdep_assert_rq_held(rq); + assert_clock_updated(rq); + + return rq->clock_pelt - rq->lost_idle_time; +} + +/* The rq is idle, we can sync to clock_task */ +static inline void _update_idle_rq_clock_pelt(struct rq *rq) +{ + rq->clock_pelt =3D rq_clock_task(rq); + + u64_u32_store(rq->enter_idle, rq_clock(rq)); + u64_u32_store(rq->clock_pelt_idle, rq_clock_pelt(rq)); +} + /* * The clock_pelt scales the time to reflect the effective amount of * computation done during the running delta time but then sync back to @@ -76,8 +93,7 @@ static inline void cfs_se_util_change(struct sched_avg *a= vg) static inline void update_rq_clock_pelt(struct rq *rq, s64 delta) { if (unlikely(is_idle_task(rq->curr))) { - /* The rq is idle, we can sync to clock_task */ - rq->clock_pelt =3D rq_clock_task(rq); + _update_idle_rq_clock_pelt(rq); return; } =20 @@ -130,17 +146,26 @@ static inline void update_idle_rq_clock_pelt(struct r= q *rq) */ if (util_sum >=3D divider) rq->lost_idle_time +=3D rq_clock_task(rq) - rq->clock_pelt; + + _update_idle_rq_clock_pelt(rq); } =20 -static inline u64 rq_clock_pelt(struct rq *rq) +#ifdef CONFIG_CFS_BANDWIDTH +static inline void update_idle_cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { - lockdep_assert_rq_held(rq); - assert_clock_updated(rq); - - return rq->clock_pelt - rq->lost_idle_time; + /* + * Make sure that pending update of rq->clock_pelt_idle and + * rq->enter_idle are visible during update_blocked_average() before + * updating cfs_rq->throttled_pelt_idle. + */ + smp_wmb(); + if (unlikely(cfs_rq->throttle_count)) + u64_u32_store(cfs_rq->throttled_pelt_idle, U64_MAX); + else + u64_u32_store(cfs_rq->throttled_pelt_idle, + cfs_rq->throttled_clock_pelt_time); } =20 -#ifdef CONFIG_CFS_BANDWIDTH /* rq->task_clock normalized against any time this cfs_rq has spent thrott= led */ static inline u64 cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { @@ -150,6 +175,7 @@ static inline u64 cfs_rq_clock_pelt(struct cfs_rq *cfs_= rq) return rq_clock_pelt(rq_of(cfs_rq)) - cfs_rq->throttled_clock_pelt_time; } #else +static inline void update_idle_cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { } static inline u64 cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { return rq_clock_pelt(rq_of(cfs_rq)); @@ -204,6 +230,7 @@ update_rq_clock_pelt(struct rq *rq, s64 delta) { } static inline void update_idle_rq_clock_pelt(struct rq *rq) { } =20 +static inline void update_idle_cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { } #endif =20 =20 diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index e2cf6e48b165..ea9365e1a24e 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -641,6 +641,10 @@ struct cfs_rq { int runtime_enabled; s64 runtime_remaining; =20 + u64 throttled_pelt_idle; +#ifndef CONFIG_64BIT + u64 throttled_pelt_idle_copy; +#endif u64 throttled_clock; u64 throttled_clock_pelt; u64 throttled_clock_pelt_time; @@ -1013,6 +1017,12 @@ struct rq { u64 clock_task ____cacheline_aligned; u64 clock_pelt; unsigned long lost_idle_time; + u64 clock_pelt_idle; + u64 enter_idle; +#ifndef CONFIG_64BIT + u64 clock_pelt_idle_copy; + u64 enter_idle_copy; +#endif =20 atomic_t nr_iowait; =20 --=20 2.25.1 From nobody Sun May 10 15:45:29 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54734C433EF for ; Fri, 29 Apr 2022 14:13:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376910AbiD2OQj (ORCPT ); Fri, 29 Apr 2022 10:16:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376604AbiD2OQ0 (ORCPT ); Fri, 29 Apr 2022 10:16:26 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id ECA4D1A836 for ; Fri, 29 Apr 2022 07:13:07 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AC4C61474; Fri, 29 Apr 2022 07:13:07 -0700 (PDT) Received: from localhost.localdomain (FVFF7649Q05P.cambridge.arm.com [10.1.32.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 661383F774; Fri, 29 Apr 2022 07:13:06 -0700 (PDT) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, qperret@google.com, tao.zhou@linux.dev Subject: [PATCH v8 3/7] sched, drivers: Remove max param from effective_cpu_util()/sched_cpu_util() Date: Fri, 29 Apr 2022 15:11:44 +0100 Message-Id: <20220429141148.181816-4-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220429141148.181816-1-vincent.donnefort@arm.com> References: <20220429141148.181816-1-vincent.donnefort@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Dietmar Eggemann effective_cpu_util() already has a `int cpu' parameter which allows to retrieve the CPU capacity scale factor (or maximum CPU capacity) inside this function via an arch_scale_cpu_capacity(cpu). A lot of code calling effective_cpu_util() (or the shim sched_cpu_util()) needs the maximum CPU capacity, i.e. it will call arch_scale_cpu_capacity() already. But not having to pass it into effective_cpu_util() will make the EAS wake-up code easier, especially when the maximum CPU capacity reduced by the thermal pressure is passed through the EAS wake-up functions. Due to the asymmetric CPU capacity support of arm/arm64 architectures, arch_scale_cpu_capacity(int cpu) is a per-CPU variable read access via per_cpu(cpu_scale, cpu) on such a system. On all other architectures it is a a compile-time constant (SCHED_CAPACITY_SCALE). Signed-off-by: Dietmar Eggemann diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c index bca2f912d349..024dba4e6575 100644 --- a/drivers/powercap/dtpm_cpu.c +++ b/drivers/powercap/dtpm_cpu.c @@ -71,34 +71,19 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 po= wer_limit) =20 static u64 scale_pd_power_uw(struct cpumask *pd_mask, u64 power) { - unsigned long max =3D 0, sum_util =3D 0; + unsigned long max, sum_util =3D 0; int cpu; =20 - for_each_cpu_and(cpu, pd_mask, cpu_online_mask) { - - /* - * The capacity is the same for all CPUs belonging to - * the same perf domain, so a single call to - * arch_scale_cpu_capacity() is enough. However, we - * need the CPU parameter to be initialized by the - * loop, so the call ends up in this block. - * - * We can initialize 'max' with a cpumask_first() call - * before the loop but the bits computation is not - * worth given the arch_scale_cpu_capacity() just - * returns a value where the resulting assembly code - * will be optimized by the compiler. - */ - max =3D arch_scale_cpu_capacity(cpu); - sum_util +=3D sched_cpu_util(cpu, max); - } - /* - * In the improbable case where all the CPUs of the perf - * domain are offline, 'max' will be zero and will lead to an - * illegal operation with a zero division. + * The capacity is the same for all CPUs belonging to + * the same perf domain. */ - return max ? (power * ((sum_util << 10) / max)) >> 10 : 0; + max =3D arch_scale_cpu_capacity(cpumask_first(pd_mask)); + + for_each_cpu_and(cpu, pd_mask, cpu_online_mask) + sum_util +=3D sched_cpu_util(cpu); + + return (power * ((sum_util << 10) / max)) >> 10; } =20 static u64 get_pd_power_uw(struct dtpm *dtpm) diff --git a/drivers/thermal/cpufreq_cooling.c b/drivers/thermal/cpufreq_co= oling.c index 0bfb8eebd126..3f514ff3d9aa 100644 --- a/drivers/thermal/cpufreq_cooling.c +++ b/drivers/thermal/cpufreq_cooling.c @@ -137,11 +137,9 @@ static u32 cpu_power_to_freq(struct cpufreq_cooling_de= vice *cpufreq_cdev, static u32 get_load(struct cpufreq_cooling_device *cpufreq_cdev, int cpu, int cpu_idx) { - unsigned long max =3D arch_scale_cpu_capacity(cpu); - unsigned long util; + unsigned long util =3D sched_cpu_util(cpu); =20 - util =3D sched_cpu_util(cpu, max); - return (util * 100) / max; + return (util * 100) / arch_scale_cpu_capacity(cpu); } #else /* !CONFIG_SMP */ static u32 get_load(struct cpufreq_cooling_device *cpufreq_cdev, int cpu, diff --git a/include/linux/sched.h b/include/linux/sched.h index 67f06f72c50e..c1705effb3a4 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2255,7 +2255,7 @@ static inline bool owner_on_cpu(struct task_struct *o= wner) } =20 /* Returns effective CPU energy utilization, as seen by the scheduler */ -unsigned long sched_cpu_util(int cpu, unsigned long max); +unsigned long sched_cpu_util(int cpu); #endif /* CONFIG_SMP */ =20 #ifdef CONFIG_RSEQ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 068c088e9584..a62d25ec5b0d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7061,12 +7061,14 @@ struct task_struct *idle_task(int cpu) * required to meet deadlines. */ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs, - unsigned long max, enum cpu_util_type type, + enum cpu_util_type type, struct task_struct *p) { - unsigned long dl_util, util, irq; + unsigned long dl_util, util, irq, max; struct rq *rq =3D cpu_rq(cpu); =20 + max =3D arch_scale_cpu_capacity(cpu); + if (!uclamp_is_used() && type =3D=3D FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt)) { return max; @@ -7146,10 +7148,9 @@ unsigned long effective_cpu_util(int cpu, unsigned l= ong util_cfs, return min(max, util); } =20 -unsigned long sched_cpu_util(int cpu, unsigned long max) +unsigned long sched_cpu_util(int cpu) { - return effective_cpu_util(cpu, cpu_util_cfs(cpu), max, - ENERGY_UTIL, NULL); + return effective_cpu_util(cpu, cpu_util_cfs(cpu), ENERGY_UTIL, NULL); } #endif /* CONFIG_SMP */ =20 diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedu= til.c index 3dbf351d12d5..1207c78f85c1 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -157,11 +157,10 @@ static unsigned int get_next_freq(struct sugov_policy= *sg_policy, static void sugov_get_util(struct sugov_cpu *sg_cpu) { struct rq *rq =3D cpu_rq(sg_cpu->cpu); - unsigned long max =3D arch_scale_cpu_capacity(sg_cpu->cpu); =20 - sg_cpu->max =3D max; + sg_cpu->max =3D arch_scale_cpu_capacity(sg_cpu->cpu); sg_cpu->bw_dl =3D cpu_bw_dl(rq); - sg_cpu->util =3D effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu= ), max, + sg_cpu->util =3D effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu= ), FREQUENCY_UTIL, NULL); } =20 diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 4e9e0d453a00..2d5ae9cac7f9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6729,12 +6729,11 @@ static long compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd) { struct cpumask *pd_mask =3D perf_domain_span(pd); - unsigned long cpu_cap =3D arch_scale_cpu_capacity(cpumask_first(pd_mask)); - unsigned long max_util =3D 0, sum_util =3D 0; - unsigned long _cpu_cap =3D cpu_cap; + unsigned long max_util =3D 0, sum_util =3D 0, cpu_cap; int cpu; =20 - _cpu_cap -=3D arch_scale_thermal_pressure(cpumask_first(pd_mask)); + cpu_cap =3D arch_scale_cpu_capacity(cpumask_first(pd_mask)); + cpu_cap -=3D arch_scale_thermal_pressure(cpumask_first(pd_mask)); =20 /* * The capacity state of CPUs of the current rd can be driven by CPUs @@ -6771,10 +6770,10 @@ compute_energy(struct task_struct *p, int dst_cpu, = struct perf_domain *pd) * is already enough to scale the EM reported power * consumption at the (eventually clamped) cpu_capacity. */ - cpu_util =3D effective_cpu_util(cpu, util_running, cpu_cap, - ENERGY_UTIL, NULL); + cpu_util =3D effective_cpu_util(cpu, util_running, ENERGY_UTIL, + NULL); =20 - sum_util +=3D min(cpu_util, _cpu_cap); + sum_util +=3D min(cpu_util, cpu_cap); =20 /* * Performance domain frequency: utilization clamping @@ -6783,12 +6782,12 @@ compute_energy(struct task_struct *p, int dst_cpu, = struct perf_domain *pd) * NOTE: in case RT tasks are running, by default the * FREQUENCY_UTIL's utilization can be max OPP. */ - cpu_util =3D effective_cpu_util(cpu, util_freq, cpu_cap, - FREQUENCY_UTIL, tsk); - max_util =3D max(max_util, min(cpu_util, _cpu_cap)); + cpu_util =3D effective_cpu_util(cpu, util_freq, FREQUENCY_UTIL, + tsk); + max_util =3D max(max_util, min(cpu_util, cpu_cap)); } =20 - return em_cpu_energy(pd->em_pd, max_util, sum_util, _cpu_cap); + return em_cpu_energy(pd->em_pd, max_util, sum_util, cpu_cap); } =20 /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index ea9365e1a24e..c33d4fc3c80d 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2878,7 +2878,7 @@ enum cpu_util_type { }; =20 unsigned long effective_cpu_util(int cpu, unsigned long util_cfs, - unsigned long max, enum cpu_util_type type, + enum cpu_util_type type, struct task_struct *p); =20 static inline unsigned long cpu_bw_dl(struct rq *rq) --=20 2.25.1 From nobody Sun May 10 15:45:29 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A350DC433EF for ; Fri, 29 Apr 2022 14:13:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377105AbiD2OQp (ORCPT ); Fri, 29 Apr 2022 10:16:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376741AbiD2OQ2 (ORCPT ); Fri, 29 Apr 2022 10:16:28 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 75C5520F65 for ; Fri, 29 Apr 2022 07:13:09 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2A2541477; Fri, 29 Apr 2022 07:13:09 -0700 (PDT) Received: from localhost.localdomain (FVFF7649Q05P.cambridge.arm.com [10.1.32.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id E43353F774; Fri, 29 Apr 2022 07:13:07 -0700 (PDT) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, qperret@google.com, tao.zhou@linux.dev Subject: [PATCH v8 4/7] sched/fair: Rename select_idle_mask to select_rq_mask Date: Fri, 29 Apr 2022 15:11:45 +0100 Message-Id: <20220429141148.181816-5-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220429141148.181816-1-vincent.donnefort@arm.com> References: <20220429141148.181816-1-vincent.donnefort@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Dietmar Eggemann Decouple the name of the per-cpu cpumask select_idle_mask from its usage in select_idle_[cpu/capacity]() of the CFS run-queue selection (select_task_rq_fair()). This is to support the reuse of this cpumask in the Energy Aware Scheduling (EAS) path (find_energy_efficient_cpu()) of the CFS run-queue selection. Signed-off-by: Dietmar Eggemann diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a62d25ec5b0d..f3f5540bae9e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -9456,7 +9456,7 @@ static struct kmem_cache *task_group_cache __read_mos= tly; #endif =20 DECLARE_PER_CPU(cpumask_var_t, load_balance_mask); -DECLARE_PER_CPU(cpumask_var_t, select_idle_mask); +DECLARE_PER_CPU(cpumask_var_t, select_rq_mask); =20 void __init sched_init(void) { @@ -9505,7 +9505,7 @@ void __init sched_init(void) for_each_possible_cpu(i) { per_cpu(load_balance_mask, i) =3D (cpumask_var_t)kzalloc_node( cpumask_size(), GFP_KERNEL, cpu_to_node(i)); - per_cpu(select_idle_mask, i) =3D (cpumask_var_t)kzalloc_node( + per_cpu(select_rq_mask, i) =3D (cpumask_var_t)kzalloc_node( cpumask_size(), GFP_KERNEL, cpu_to_node(i)); } #endif /* CONFIG_CPUMASK_OFFSTACK */ diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2d5ae9cac7f9..c1c63322836a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5880,7 +5880,7 @@ static void dequeue_task_fair(struct rq *rq, struct t= ask_struct *p, int flags) =20 /* Working cpumask for: load_balance, load_balance_newidle. */ DEFINE_PER_CPU(cpumask_var_t, load_balance_mask); -DEFINE_PER_CPU(cpumask_var_t, select_idle_mask); +DEFINE_PER_CPU(cpumask_var_t, select_rq_mask); =20 #ifdef CONFIG_NO_HZ_COMMON =20 @@ -6370,7 +6370,7 @@ static inline int select_idle_smt(struct task_struct = *p, struct sched_domain *sd */ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd,= bool has_idle_core, int target) { - struct cpumask *cpus =3D this_cpu_cpumask_var_ptr(select_idle_mask); + struct cpumask *cpus =3D this_cpu_cpumask_var_ptr(select_rq_mask); int i, cpu, idle_cpu =3D -1, nr =3D INT_MAX; struct rq *this_rq =3D this_rq(); int this =3D smp_processor_id(); @@ -6456,7 +6456,7 @@ select_idle_capacity(struct task_struct *p, struct sc= hed_domain *sd, int target) int cpu, best_cpu =3D -1; struct cpumask *cpus; =20 - cpus =3D this_cpu_cpumask_var_ptr(select_idle_mask); + cpus =3D this_cpu_cpumask_var_ptr(select_rq_mask); cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); =20 task_util =3D uclamp_task_util(p); --=20 2.25.1 From nobody Sun May 10 15:45:29 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65142C433EF for ; Fri, 29 Apr 2022 14:13:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377139AbiD2OQv (ORCPT ); Fri, 29 Apr 2022 10:16:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376824AbiD2OQ3 (ORCPT ); Fri, 29 Apr 2022 10:16:29 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DD8B020F68 for ; Fri, 29 Apr 2022 07:13:10 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9E04A14BF; Fri, 29 Apr 2022 07:13:10 -0700 (PDT) Received: from localhost.localdomain (FVFF7649Q05P.cambridge.arm.com [10.1.32.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 5FA4E3F774; Fri, 29 Apr 2022 07:13:09 -0700 (PDT) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, qperret@google.com, tao.zhou@linux.dev Subject: [PATCH v8 5/7] sched/fair: Use the same cpumask per-PD throughout find_energy_efficient_cpu() Date: Fri, 29 Apr 2022 15:11:46 +0100 Message-Id: <20220429141148.181816-6-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220429141148.181816-1-vincent.donnefort@arm.com> References: <20220429141148.181816-1-vincent.donnefort@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Dietmar Eggemann The Perf Domain (PD) cpumask (struct em_perf_domain.cpus) stays invariant after Energy Model creation, i.e. it is not updated after CPU hotplug operations. That's why the PD mask is used in conjunction with the cpu_online_mask (or Sched Domain cpumask). Thereby the cpu_online_mask is fetched multiple times (in compute_energy()) during a run-queue selection for a task. cpu_online_mask may change during this time which can lead to wrong energy calculations. To be able to avoid this, use the select_rq_mask per-cpu cpumask to create a cpumask out of PD cpumask and cpu_online_mask and pass it through the function calls of the EAS run-queue selection path. The PD cpumask for max_spare_cap_cpu/compute_prev_delta selection (find_energy_efficient_cpu()) is now ANDed not only with the SD mask but also with the cpu_online_mask. This is fine since this cpumask has to be in syc with the one used for energy computation (compute_energy()). An exclusive cpuset setup with at least one asymmetric CPU capacity island (hence the additional AND with the SD cpumask) is the obvious exception here. Signed-off-by: Dietmar Eggemann diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c1c63322836a..684e89a0f694 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6726,14 +6726,14 @@ static unsigned long cpu_util_next(int cpu, struct = task_struct *p, int dst_cpu) * task. */ static long -compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd) +compute_energy(struct task_struct *p, int dst_cpu, struct cpumask *cpus, + struct perf_domain *pd) { - struct cpumask *pd_mask =3D perf_domain_span(pd); unsigned long max_util =3D 0, sum_util =3D 0, cpu_cap; int cpu; =20 - cpu_cap =3D arch_scale_cpu_capacity(cpumask_first(pd_mask)); - cpu_cap -=3D arch_scale_thermal_pressure(cpumask_first(pd_mask)); + cpu_cap =3D arch_scale_cpu_capacity(cpumask_first(cpus)); + cpu_cap -=3D arch_scale_thermal_pressure(cpumask_first(cpus)); =20 /* * The capacity state of CPUs of the current rd can be driven by CPUs @@ -6744,7 +6744,7 @@ compute_energy(struct task_struct *p, int dst_cpu, st= ruct perf_domain *pd) * If an entire pd is outside of the current rd, it will not appear in * its pd list and will not be accounted by compute_energy(). */ - for_each_cpu_and(cpu, pd_mask, cpu_online_mask) { + for_each_cpu(cpu, cpus) { unsigned long util_freq =3D cpu_util_next(cpu, p, dst_cpu); unsigned long cpu_util, util_running =3D util_freq; struct task_struct *tsk =3D NULL; @@ -6831,6 +6831,7 @@ compute_energy(struct task_struct *p, int dst_cpu, st= ruct perf_domain *pd) */ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) { + struct cpumask *cpus =3D this_cpu_cpumask_var_ptr(select_rq_mask); unsigned long prev_delta =3D ULONG_MAX, best_delta =3D ULONG_MAX; struct root_domain *rd =3D cpu_rq(smp_processor_id())->rd; int cpu, best_energy_cpu =3D prev_cpu, target =3D -1; @@ -6865,7 +6866,9 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) unsigned long base_energy_pd; int max_spare_cap_cpu =3D -1; =20 - for_each_cpu_and(cpu, perf_domain_span(pd), sched_domain_span(sd)) { + cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask); + + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) { if (!cpumask_test_cpu(cpu, p->cpus_ptr)) continue; =20 @@ -6902,12 +6905,12 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) continue; =20 /* Compute the 'base' energy of the pd, without @p */ - base_energy_pd =3D compute_energy(p, -1, pd); + base_energy_pd =3D compute_energy(p, -1, cpus, pd); base_energy +=3D base_energy_pd; =20 /* Evaluate the energy impact of using prev_cpu. */ if (compute_prev_delta) { - prev_delta =3D compute_energy(p, prev_cpu, pd); + prev_delta =3D compute_energy(p, prev_cpu, cpus, pd); if (prev_delta < base_energy_pd) goto unlock; prev_delta -=3D base_energy_pd; @@ -6916,7 +6919,8 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) =20 /* Evaluate the energy impact of using max_spare_cap_cpu. */ if (max_spare_cap_cpu >=3D 0) { - cur_delta =3D compute_energy(p, max_spare_cap_cpu, pd); + cur_delta =3D compute_energy(p, max_spare_cap_cpu, cpus, + pd); if (cur_delta < base_energy_pd) goto unlock; cur_delta -=3D base_energy_pd; --=20 2.25.1 From nobody Sun May 10 15:45:29 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4EA70C433F5 for ; Fri, 29 Apr 2022 14:13:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376867AbiD2OQy (ORCPT ); Fri, 29 Apr 2022 10:16:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47592 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376911AbiD2OQc (ORCPT ); Fri, 29 Apr 2022 10:16:32 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6F66427CE7 for ; Fri, 29 Apr 2022 07:13:12 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 409F6150C; Fri, 29 Apr 2022 07:13:12 -0700 (PDT) Received: from localhost.localdomain (FVFF7649Q05P.cambridge.arm.com [10.1.32.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id D6CE63F774; Fri, 29 Apr 2022 07:13:10 -0700 (PDT) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, qperret@google.com, tao.zhou@linux.dev, Vincent Donnefort Subject: [PATCH v8 6/7] sched/fair: Remove task_util from effective utilization in feec() Date: Fri, 29 Apr 2022 15:11:47 +0100 Message-Id: <20220429141148.181816-7-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220429141148.181816-1-vincent.donnefort@arm.com> References: <20220429141148.181816-1-vincent.donnefort@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The energy estimation in find_energy_efficient_cpu() (feec()) relies on the computation of the effective utilization for each CPU of a perf domain (PD). This effective utilization is then used as an estimation of the busy time for this pd. The function effective_cpu_util() which gives this value, scales the utilization relative to IRQ pressure on the CPU to take into account that the IRQ time is hidden from the task clock. The IRQ scaling is as follow: effective_cpu_util =3D irq + (cpu_cap - irq)/cpu_cap * util Where util is the sum of CFS/RT/DL utilization, cpu_cap the capacity of the CPU and irq the IRQ avg time. If now we take as an example a task placement which doesn't raise the OPP on the candidate CPU, we can write the energy delta as: delta =3D OPPcost/cpu_cap * (effective_cpu_util(cpu_util + task_util) - effective_cpu_util(cpu_util)) =3D OPPcost/cpu_cap * (cpu_cap - irq)/cpu_cap * task_util We end-up with an energy delta depending on the IRQ avg time, which is a problem: first the time spent on IRQs by a CPU has no effect on the additional energy that would be consumed by a task. Second, we don't want to favour a CPU with a higher IRQ avg time value. Nonetheless, we need to take the IRQ avg time into account. If a task placement raises the PD's frequency, it will increase the energy cost for the entire time where the CPU is busy. A solution is to only use effective_cpu_util() with the CPU contribution part. The task contribution is added separately and scaled according to prev_cpu's IRQ time. No change for the FREQUENCY_UTIL component of the energy estimation. We still want to get the actual frequency that would be selected after the task placement. Signed-off-by: Vincent Donnefort diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 684e89a0f694..83a6eb99d938 100644 Reviewed-by: Dietmar Eggemann --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6719,61 +6719,97 @@ static unsigned long cpu_util_next(int cpu, struct = task_struct *p, int dst_cpu) } =20 /* - * compute_energy(): Estimates the energy that @pd would consume if @p was - * migrated to @dst_cpu. compute_energy() predicts what will be the utiliz= ation - * landscape of @pd's CPUs after the task migration, and uses the Energy M= odel - * to compute what would be the energy if we decided to actually migrate t= hat - * task. + * energy_env - Utilization landscape for energy estimation. + * @task_busy_time: Utilization contribution by the task for which we test= the + * placement. Given by eenv_task_busy_time(). + * @pd_busy_time: Utilization of the whole perf domain without the task + * contribution. Given by eenv_pd_busy_time(). + * @cpu_cap: Maximum CPU capacity for the perf domain. + * @pd_cap: Entire perf domain capacity. (pd->nr_cpus * cpu_cap). + */ +struct energy_env { + unsigned long task_busy_time; + unsigned long pd_busy_time; + unsigned long cpu_cap; + unsigned long pd_cap; +}; + +/* + * Compute the task busy time for compute_energy(). This time cannot be + * injected directly into effective_cpu_util() because of the IRQ scaling. + * The latter only makes sense with the most recent CPUs where the task has + * run. */ -static long -compute_energy(struct task_struct *p, int dst_cpu, struct cpumask *cpus, - struct perf_domain *pd) +static inline void eenv_task_busy_time(struct energy_env *eenv, + struct task_struct *p, int prev_cpu) { - unsigned long max_util =3D 0, sum_util =3D 0, cpu_cap; + unsigned long max_cap =3D arch_scale_cpu_capacity(prev_cpu); + unsigned long irq =3D cpu_util_irq(cpu_rq(prev_cpu)); + + if (unlikely(irq >=3D max_cap)) { + eenv->task_busy_time =3D max_cap; + return; + } + + eenv->task_busy_time =3D + scale_irq_capacity(task_util_est(p), irq, max_cap); +} + +/* + * Compute the perf_domain (PD) busy time for compute_energy(). Based on t= he + * utilization for each @pd_cpus, it however doesn't take into account + * clamping since the ratio (utilization / cpu_capacity) is already enough= to + * scale the EM reported power consumption at the (eventually clamped) + * cpu_capacity. + * + * The contribution of the task @p for which we want to estimate the + * energy cost is removed (by cpu_util_next()) and must be calculated + * separately (see eenv_task_busy_time). This ensures: + * + * - A stable PD utilization, no matter which CPU of that PD we want to = place + * the task on. + * + * - A fair comparison between CPUs as the task contribution (task_util(= )) + * will always be the same no matter which CPU utilization we rely on + * (util_avg or util_est). + * + * Set @eenv busy time for the PD that spans @pd_cpus. This busy time can't + * exceed @eenv->pd_cap. + */ +static inline void eenv_pd_busy_time(struct energy_env *eenv, + struct cpumask *pd_cpus, + struct task_struct *p) +{ + unsigned long busy_time =3D 0; int cpu; =20 - cpu_cap =3D arch_scale_cpu_capacity(cpumask_first(cpus)); - cpu_cap -=3D arch_scale_thermal_pressure(cpumask_first(cpus)); + for_each_cpu(cpu, pd_cpus) { + unsigned long util =3D cpu_util_next(cpu, p, -1); =20 - /* - * The capacity state of CPUs of the current rd can be driven by CPUs - * of another rd if they belong to the same pd. So, account for the - * utilization of these CPUs too by masking pd with cpu_online_mask - * instead of the rd span. - * - * If an entire pd is outside of the current rd, it will not appear in - * its pd list and will not be accounted by compute_energy(). - */ - for_each_cpu(cpu, cpus) { - unsigned long util_freq =3D cpu_util_next(cpu, p, dst_cpu); - unsigned long cpu_util, util_running =3D util_freq; - struct task_struct *tsk =3D NULL; + busy_time +=3D effective_cpu_util(cpu, util, ENERGY_UTIL, NULL); + } =20 - /* - * When @p is placed on @cpu: - * - * util_running =3D max(cpu_util, cpu_util_est) + - * max(task_util, _task_util_est) - * - * while cpu_util_next is: max(cpu_util + task_util, - * cpu_util_est + _task_util_est) - */ - if (cpu =3D=3D dst_cpu) { - tsk =3D p; - util_running =3D - cpu_util_next(cpu, p, -1) + task_util_est(p); - } + eenv->pd_busy_time =3D min(eenv->pd_cap, busy_time); +} =20 - /* - * Busy time computation: utilization clamping is not - * required since the ratio (sum_util / cpu_capacity) - * is already enough to scale the EM reported power - * consumption at the (eventually clamped) cpu_capacity. - */ - cpu_util =3D effective_cpu_util(cpu, util_running, ENERGY_UTIL, - NULL); +/* + * Compute the maximum utilization for compute_energy() when the task @p + * is placed on the cpu @dst_cpu. + * + * Returns the maximum utilization among @eenv->cpus. This utilization can= 't + * exceed @eenv->cpu_cap. + */ +static inline unsigned long +eenv_pd_max_util(struct energy_env *eenv, struct cpumask *pd_cpus, + struct task_struct *p, int dst_cpu) +{ + unsigned long max_util =3D 0; + int cpu; =20 - sum_util +=3D min(cpu_util, cpu_cap); + for_each_cpu(cpu, pd_cpus) { + struct task_struct *tsk =3D (cpu =3D=3D dst_cpu) ? p : NULL; + unsigned long util =3D cpu_util_next(cpu, p, dst_cpu); + unsigned long cpu_util; =20 /* * Performance domain frequency: utilization clamping @@ -6782,12 +6818,30 @@ compute_energy(struct task_struct *p, int dst_cpu, = struct cpumask *cpus, * NOTE: in case RT tasks are running, by default the * FREQUENCY_UTIL's utilization can be max OPP. */ - cpu_util =3D effective_cpu_util(cpu, util_freq, FREQUENCY_UTIL, - tsk); - max_util =3D max(max_util, min(cpu_util, cpu_cap)); + cpu_util =3D effective_cpu_util(cpu, util, FREQUENCY_UTIL, tsk); + max_util =3D max(max_util, cpu_util); } =20 - return em_cpu_energy(pd->em_pd, max_util, sum_util, cpu_cap); + return min(max_util, eenv->cpu_cap); +} + +/* + * compute_energy(): Use the Energy Model to estimate the energy that @pd = would + * consume for a given utilization landscape @eenv. If @dst_cpu < 0 the ta= sk + * contribution is removed from the energy estimation. + */ +static inline unsigned long +compute_energy(struct energy_env *eenv, struct perf_domain *pd, + struct cpumask *pd_cpus, struct task_struct *p, int dst_cpu) +{ + unsigned long max_util =3D eenv_pd_max_util(eenv, pd_cpus, p, dst_cpu); + unsigned long busy_time =3D eenv->pd_busy_time; + + if (dst_cpu >=3D 0) + busy_time =3D min(eenv->pd_cap, + eenv->pd_busy_time + eenv->task_busy_time); + + return em_cpu_energy(pd->em_pd, max_util, busy_time, eenv->cpu_cap); } =20 /* @@ -6833,11 +6887,12 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) { struct cpumask *cpus =3D this_cpu_cpumask_var_ptr(select_rq_mask); unsigned long prev_delta =3D ULONG_MAX, best_delta =3D ULONG_MAX; - struct root_domain *rd =3D cpu_rq(smp_processor_id())->rd; int cpu, best_energy_cpu =3D prev_cpu, target =3D -1; - unsigned long cpu_cap, util, base_energy =3D 0; + struct root_domain *rd =3D this_rq()->rd; + unsigned long base_energy =3D 0; struct sched_domain *sd; struct perf_domain *pd; + struct energy_env eenv; =20 rcu_read_lock(); pd =3D rcu_dereference(rd->pd); @@ -6860,22 +6915,36 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) if (!task_util_est(p)) goto unlock; =20 + eenv_task_busy_time(&eenv, p, prev_cpu); + for (; pd; pd =3D pd->next) { - unsigned long cur_delta, spare_cap, max_spare_cap =3D 0; + unsigned long cpu_cap, cpu_thermal_cap, util; + unsigned long cur_delta, max_spare_cap =3D 0; bool compute_prev_delta =3D false; unsigned long base_energy_pd; int max_spare_cap_cpu =3D -1; =20 cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask); =20 - for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) { + /* Account thermal pressure for the energy estimation */ + cpu =3D cpumask_first(cpus); + cpu_thermal_cap =3D arch_scale_cpu_capacity(cpu); + cpu_thermal_cap -=3D arch_scale_thermal_pressure(cpu); + + eenv.cpu_cap =3D cpu_thermal_cap; + eenv.pd_cap =3D 0; + + for_each_cpu(cpu, cpus) { + eenv.pd_cap +=3D cpu_thermal_cap; + + if (!cpumask_test_cpu(cpu, sched_domain_span(sd))) + continue; + if (!cpumask_test_cpu(cpu, p->cpus_ptr)) continue; =20 util =3D cpu_util_next(cpu, p, cpu); cpu_cap =3D capacity_of(cpu); - spare_cap =3D cpu_cap; - lsub_positive(&spare_cap, util); =20 /* * Skip CPUs that cannot satisfy the capacity request. @@ -6888,15 +6957,17 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) if (!fits_capacity(util, cpu_cap)) continue; =20 + lsub_positive(&cpu_cap, util); + if (cpu =3D=3D prev_cpu) { /* Always use prev_cpu as a candidate. */ compute_prev_delta =3D true; - } else if (spare_cap > max_spare_cap) { + } else if (cpu_cap > max_spare_cap) { /* * Find the CPU with the maximum spare capacity * in the performance domain. */ - max_spare_cap =3D spare_cap; + max_spare_cap =3D cpu_cap; max_spare_cap_cpu =3D cpu; } } @@ -6905,12 +6976,14 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) continue; =20 /* Compute the 'base' energy of the pd, without @p */ - base_energy_pd =3D compute_energy(p, -1, cpus, pd); + eenv_pd_busy_time(&eenv, cpus, p); + base_energy_pd =3D compute_energy(&eenv, pd, cpus, p, -1); base_energy +=3D base_energy_pd; =20 /* Evaluate the energy impact of using prev_cpu. */ if (compute_prev_delta) { - prev_delta =3D compute_energy(p, prev_cpu, cpus, pd); + prev_delta =3D compute_energy(&eenv, pd, cpus, p, + prev_cpu); if (prev_delta < base_energy_pd) goto unlock; prev_delta -=3D base_energy_pd; @@ -6919,8 +6992,8 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) =20 /* Evaluate the energy impact of using max_spare_cap_cpu. */ if (max_spare_cap_cpu >=3D 0) { - cur_delta =3D compute_energy(p, max_spare_cap_cpu, cpus, - pd); + cur_delta =3D compute_energy(&eenv, pd, cpus, p, + max_spare_cap_cpu); if (cur_delta < base_energy_pd) goto unlock; cur_delta -=3D base_energy_pd; --=20 2.25.1 From nobody Sun May 10 15:45:29 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6B373C433EF for ; Fri, 29 Apr 2022 14:13:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377070AbiD2OQ7 (ORCPT ); Fri, 29 Apr 2022 10:16:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376814AbiD2OQd (ORCPT ); Fri, 29 Apr 2022 10:16:33 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A92972CCBB for ; Fri, 29 Apr 2022 07:13:14 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D8E9F1063; Fri, 29 Apr 2022 07:13:13 -0700 (PDT) Received: from localhost.localdomain (FVFF7649Q05P.cambridge.arm.com [10.1.32.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 7CA913F774; Fri, 29 Apr 2022 07:13:12 -0700 (PDT) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, qperret@google.com, tao.zhou@linux.dev, Vincent Donnefort Subject: [PATCH v8 7/7] sched/fair: Remove the energy margin in feec() Date: Fri, 29 Apr 2022 15:11:48 +0100 Message-Id: <20220429141148.181816-8-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220429141148.181816-1-vincent.donnefort@arm.com> References: <20220429141148.181816-1-vincent.donnefort@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" find_energy_efficient_cpu() integrates a margin to protect tasks from bouncing back and forth from a CPU to another. This margin is set as being 6% of the total current energy estimated on the system. This however does not work for two reasons: 1. The energy estimation is not a good absolute value: compute_energy() used in feec() is a good estimation for task placement as it allows to compare the energy with and without a task. The computed delta will give a good overview of the cost for a certain task placement. It, however, doesn't work as an absolute estimation for the total energy of the system. First it adds the contribution to idle CPUs into the energy, second it mixes util_avg with util_est values. util_avg contains the near history for a CPU usage, it doesn't tell at all what the current utilization is. A system that has been quite busy in the near past will hold a very high energy and then a high margin preventing any task migration to a lower capacity CPU, wasting energy. It even creates a negative feedback loop: by holding the tasks on a less efficient CPU, the margin contributes in keeping the energy high. 2. The margin handicaps small tasks: On a system where the workload is composed mostly of small tasks (which is often the case on Android), the overall energy will be high enough to create a margin none of those tasks can cross. On a Pixel4, a small utilization of 5% on all the CPUs creates a global estimated energy of 140 joules, as per the Energy Model declaration of that same device. This means, after applying the 6% margin that any migration must save more than 8 joules to happen. No task with a utilization lower than 40 would then be able to migrate away from the biggest CPU of the system. The 6% of the overall system energy was brought by the following patch: (eb92692b2544 sched/fair: Speed-up energy-aware wake-ups) It was previously 6% of the prev_cpu energy. Also, the following one made this margin value conditional on the clusters where the task fits: (8d4c97c105ca sched/fair: Only compute base_energy_pd if necessary) We could simply revert that margin change to what it was, but the original version didn't have strong grounds neither and as demonstrated in (1.) the estimated energy isn't a good absolute value. Instead, removing it completely. It is indeed, made possible by recent changes that improved energy estimation comparison fairness (sched/fair: Remove task_util from effective utilization in feec()) (PM: EM: Increase energy calculation precision) and task utilization stabilization (sched/fair: Decay task util_avg during migration) Without a margin, we could have feared bouncing between CPUs. But running LISA's eas_behaviour test coverage on three different platforms (Hikey960, RB-5 and DB-845) showed no issue. Removing the energy margin enables more energy-optimized placements for a more energy efficient system. Signed-off-by: Vincent Donnefort diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 83a6eb99d938..97551d7be8a9 100644 Reviewed-by: Dietmar Eggemann --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6887,9 +6887,8 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) { struct cpumask *cpus =3D this_cpu_cpumask_var_ptr(select_rq_mask); unsigned long prev_delta =3D ULONG_MAX, best_delta =3D ULONG_MAX; - int cpu, best_energy_cpu =3D prev_cpu, target =3D -1; struct root_domain *rd =3D this_rq()->rd; - unsigned long base_energy =3D 0; + int cpu, best_energy_cpu, target =3D -1; struct sched_domain *sd; struct perf_domain *pd; struct energy_env eenv; @@ -6921,8 +6920,8 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) unsigned long cpu_cap, cpu_thermal_cap, util; unsigned long cur_delta, max_spare_cap =3D 0; bool compute_prev_delta =3D false; - unsigned long base_energy_pd; int max_spare_cap_cpu =3D -1; + unsigned long base_energy; =20 cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask); =20 @@ -6977,16 +6976,15 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) =20 /* Compute the 'base' energy of the pd, without @p */ eenv_pd_busy_time(&eenv, cpus, p); - base_energy_pd =3D compute_energy(&eenv, pd, cpus, p, -1); - base_energy +=3D base_energy_pd; + base_energy =3D compute_energy(&eenv, pd, cpus, p, -1); =20 /* Evaluate the energy impact of using prev_cpu. */ if (compute_prev_delta) { prev_delta =3D compute_energy(&eenv, pd, cpus, p, prev_cpu); - if (prev_delta < base_energy_pd) + if (prev_delta < base_energy) goto unlock; - prev_delta -=3D base_energy_pd; + prev_delta -=3D base_energy; best_delta =3D min(best_delta, prev_delta); } =20 @@ -6994,9 +6992,9 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) if (max_spare_cap_cpu >=3D 0) { cur_delta =3D compute_energy(&eenv, pd, cpus, p, max_spare_cap_cpu); - if (cur_delta < base_energy_pd) + if (cur_delta < base_energy) goto unlock; - cur_delta -=3D base_energy_pd; + cur_delta -=3D base_energy; if (cur_delta < best_delta) { best_delta =3D cur_delta; best_energy_cpu =3D max_spare_cap_cpu; @@ -7005,12 +7003,7 @@ static int find_energy_efficient_cpu(struct task_str= uct *p, int prev_cpu) } rcu_read_unlock(); =20 - /* - * Pick the best CPU if prev_cpu cannot be used, or if it saves at - * least 6% of the energy used by prev_cpu. - */ - if ((prev_delta =3D=3D ULONG_MAX) || - (prev_delta - best_delta) > ((prev_delta + base_energy) >> 4)) + if (best_delta < prev_delta) target =3D best_energy_cpu; =20 return target; --=20 2.25.1