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([2a01:e0a:f:6020:329b:9a6:20f4:3754]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-395cb40cd78sm6072925f8f.78.2025.03.14.09.36.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Mar 2025 09:36:23 -0700 (PDT) From: Vincent Guittot To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, lukasz.luba@arm.com, rafael.j.wysocki@intel.com, pierre.gondois@arm.com, linux-kernel@vger.kernel.org Cc: qyousef@layalina.io, hongyan.xia2@arm.com, christian.loehle@arm.com, luis.machado@arm.com, qperret@google.com, Vincent Guittot Subject: [PATCH 5/7 v6] sched/fair: Add push task mechanism for EAS Date: Fri, 14 Mar 2025 17:36:12 +0100 Message-ID: <20250314163614.1356125-6-vincent.guittot@linaro.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250314163614.1356125-1-vincent.guittot@linaro.org> References: <20250314163614.1356125-1-vincent.guittot@linaro.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" EAS is based on wakeup events to efficiently place tasks on the system, but there are cases where a task doesn't have wakeup events anymore or at a far too low pace. For such situation, we can take advantage of the task being put back in the enqueued list to check if it should be pushed on another CPU. When the task is alone on the CPU, it's never put back in the enqueued list; In this special case, we use the tick to run the check. Wake up events remain the main way to migrate tasks but we now detect situation where a task is stuck on a CPU by checking that its utilization is larger than the max available compute capacity (max cpu capacity or uclamp max setting) Signed-off-by: Vincent Guittot --- kernel/sched/fair.c | 220 +++++++++++++++++++++++++++++++++++++++++++ kernel/sched/sched.h | 2 + 2 files changed, 222 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index fa23e48c1965..9a95d2eb168e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7053,6 +7053,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *= p, int flags) hrtick_update(rq); } =20 +static void fair_remove_pushable_task(struct rq *rq, struct task_struct *p= ); static void set_next_buddy(struct sched_entity *se); =20 /* @@ -7083,6 +7084,8 @@ static int dequeue_entities(struct rq *rq, struct sch= ed_entity *se, int flags) h_nr_idle =3D task_has_idle_policy(p); if (task_sleep || task_delayed || !se->sched_delayed) h_nr_runnable =3D 1; + + fair_remove_pushable_task(rq, p); } else { cfs_rq =3D group_cfs_rq(se); slice =3D cfs_rq_min_slice(cfs_rq); @@ -8591,6 +8594,197 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) return target; } =20 +static inline bool task_stuck_on_cpu(struct task_struct *p, int cpu) +{ + unsigned long max_capa, util; + + max_capa =3D min(get_actual_cpu_capacity(cpu), + uclamp_eff_value(p, UCLAMP_MAX)); + util =3D max(task_util_est(p), task_runnable(p)); + + /* + * Return true only if the task might not sleep/wakeup because of a low + * compute capacity. Tasks, which wake up regularly, will be handled by + * feec(). + */ + return (util > max_capa); +} + +static inline bool sched_energy_push_task(struct task_struct *p, struct rq= *rq) +{ + if (p->nr_cpus_allowed =3D=3D 1) + return false; + + if (is_rd_overutilized(rq->rd)) + return false; + + if (task_stuck_on_cpu(p, cpu_of(rq))) + return true; + + return false; +} + +static int active_load_balance_cpu_stop(void *data); + +static inline void check_pushable_task(struct task_struct *p, struct rq *r= q) +{ + int new_cpu, cpu =3D cpu_of(rq); + + if (!sched_energy_enabled()) + return; + + if (WARN_ON(!p)) + return; + + if (WARN_ON(!task_current(rq, p))) + return; + + if (is_migration_disabled(p)) + return; + + /* If there are several task, wait for being put back */ + if (rq->nr_running > 1) + return; + + if (!sched_energy_push_task(p, rq)) + return; + + new_cpu =3D find_energy_efficient_cpu(p, cpu); + + if (new_cpu =3D=3D cpu) + return; + + /* + * ->active_balance synchronizes accesses to + * ->active_balance_work. Once set, it's cleared + * only after active load balance is finished. + */ + if (!rq->active_balance) { + rq->active_balance =3D 1; + rq->push_cpu =3D new_cpu; + } else + return; + + raw_spin_rq_unlock(rq); + stop_one_cpu_nowait(cpu, + active_load_balance_cpu_stop, rq, + &rq->active_balance_work); + raw_spin_rq_lock(rq); +} + +static inline int has_pushable_tasks(struct rq *rq) +{ + return !plist_head_empty(&rq->cfs.pushable_tasks); +} + +static struct task_struct *pick_next_pushable_fair_task(struct rq *rq) +{ + struct task_struct *p; + + if (!has_pushable_tasks(rq)) + return NULL; + + p =3D plist_first_entry(&rq->cfs.pushable_tasks, + struct task_struct, pushable_tasks); + + WARN_ON_ONCE(rq->cpu !=3D task_cpu(p)); + WARN_ON_ONCE(task_current(rq, p)); + WARN_ON_ONCE(p->nr_cpus_allowed <=3D 1); + WARN_ON_ONCE(!task_on_rq_queued(p)); + + /* + * Remove task from the pushable list as we try only once after that + * the task has been put back in enqueued list. + */ + plist_del(&p->pushable_tasks, &rq->cfs.pushable_tasks); + + return p; +} + +/* + * See if the non running fair tasks on this rq can be sent on other CPUs + * that fits better with their profile. + */ +static bool push_fair_task(struct rq *rq) +{ + struct task_struct *next_task; + int prev_cpu, new_cpu; + struct rq *new_rq; + + next_task =3D pick_next_pushable_fair_task(rq); + if (!next_task) + return false; + + if (is_migration_disabled(next_task)) + return true; + + /* We might release rq lock */ + get_task_struct(next_task); + + prev_cpu =3D rq->cpu; + + new_cpu =3D find_energy_efficient_cpu(next_task, prev_cpu); + + if (new_cpu =3D=3D prev_cpu) + goto out; + + new_rq =3D cpu_rq(new_cpu); + + if (double_lock_balance(rq, new_rq)) { + /* The task has already migrated in between */ + if (task_cpu(next_task) !=3D rq->cpu) { + double_unlock_balance(rq, new_rq); + goto out; + } + + deactivate_task(rq, next_task, 0); + set_task_cpu(next_task, new_cpu); + activate_task(new_rq, next_task, 0); + + resched_curr(new_rq); + + double_unlock_balance(rq, new_rq); + } + +out: + put_task_struct(next_task); + + return true; +} + +static void push_fair_tasks(struct rq *rq) +{ + /* push_fair_task() will return true if it moved a fair task */ + while (push_fair_task(rq)) + ; +} + +static DEFINE_PER_CPU(struct balance_callback, fair_push_head); + +static inline void fair_queue_pushable_tasks(struct rq *rq) +{ + if (!sched_energy_enabled() || !has_pushable_tasks(rq)) + return; + + queue_balance_callback(rq, &per_cpu(fair_push_head, rq->cpu), push_fair_t= asks); +} +static void fair_remove_pushable_task(struct rq *rq, struct task_struct *p) +{ + if (sched_energy_enabled()) + plist_del(&p->pushable_tasks, &rq->cfs.pushable_tasks); +} + +static void fair_add_pushable_task(struct rq *rq, struct task_struct *p) +{ + if (sched_energy_enabled() && task_on_rq_queued(p) && !p->se.sched_delaye= d) { + if (sched_energy_push_task(p, rq)) { + plist_del(&p->pushable_tasks, &rq->cfs.pushable_tasks); + plist_node_init(&p->pushable_tasks, p->prio); + plist_add(&p->pushable_tasks, &rq->cfs.pushable_tasks); + } + } +} + /* * select_task_rq_fair: Select target runqueue for the waking task in doma= ins * that have the relevant SD flag set. In practice, this is SD_BALANCE_WAK= E, @@ -8760,6 +8954,10 @@ balance_fair(struct rq *rq, struct task_struct *prev= , struct rq_flags *rf) return sched_balance_newidle(rq, rf) !=3D 0; } #else +static inline void check_pushable_task(struct task_struct *p, struct rq *r= q) {} +static inline void fair_queue_pushable_tasks(struct rq *rq) {} +static void fair_remove_pushable_task(struct rq *rq, struct task_struct *p= ) {} +static inline void fair_add_pushable_task(struct rq *rq, struct task_struc= t *p) {} static inline void set_task_max_allowed_capacity(struct task_struct *p) {} #endif /* CONFIG_SMP */ =20 @@ -8949,6 +9147,12 @@ pick_next_task_fair(struct rq *rq, struct task_struc= t *prev, struct rq_flags *rf put_prev_entity(cfs_rq, pse); set_next_entity(cfs_rq, se); =20 + /* + * The previous task might be eligible for being pushed on + * another cpu if it is still active. + */ + fair_add_pushable_task(rq, prev); + __set_next_task_fair(rq, p, true); } =20 @@ -9021,6 +9225,13 @@ static void put_prev_task_fair(struct rq *rq, struct= task_struct *prev, struct t cfs_rq =3D cfs_rq_of(se); put_prev_entity(cfs_rq, se); } + + /* + * The previous task might be eligible for being pushed on another cpu + * if it is still active. + */ + fair_add_pushable_task(rq, prev); + } =20 /* @@ -13151,6 +13362,7 @@ static void task_tick_fair(struct rq *rq, struct ta= sk_struct *curr, int queued) if (static_branch_unlikely(&sched_numa_balancing)) task_tick_numa(rq, curr); =20 + check_pushable_task(curr, rq); update_misfit_status(curr, rq); check_update_overutilized_status(task_rq(curr)); =20 @@ -13303,6 +13515,8 @@ static void __set_next_task_fair(struct rq *rq, str= uct task_struct *p, bool firs { struct sched_entity *se =3D &p->se; =20 + fair_remove_pushable_task(rq, p); + #ifdef CONFIG_SMP if (task_on_rq_queued(p)) { /* @@ -13320,6 +13534,11 @@ static void __set_next_task_fair(struct rq *rq, st= ruct task_struct *p, bool firs if (hrtick_enabled_fair(rq)) hrtick_start_fair(rq, p); =20 + /* + * Try to push prev task before checking misfit for next task as + * the migration of prev can make next fitting the CPU + */ + fair_queue_pushable_tasks(rq); update_misfit_status(p, rq); sched_fair_update_stop_tick(rq, p); } @@ -13350,6 +13569,7 @@ 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)); #ifdef CONFIG_SMP + plist_head_init(&cfs_rq->pushable_tasks); raw_spin_lock_init(&cfs_rq->removed.lock); #endif } diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 023b844159c9..51dd9bc55a0d 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -689,6 +689,8 @@ struct cfs_rq { unsigned long runnable_avg; } removed; =20 + struct plist_head pushable_tasks; + #ifdef CONFIG_FAIR_GROUP_SCHED u64 last_update_tg_load_avg; unsigned long tg_load_avg_contrib; --=20 2.43.0