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Date: Wed, 29 Jun 2022 16:05:49 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
rdunlap@...radead.org, vschneid@...hat.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: remove redundant cpu_cgrp_subsys->fork()
On Wed, 22 Jun 2022 at 11:48, Chengming Zhou
<zhouchengming@...edance.com> wrote:
>
> We use cpu_cgrp_subsys->fork() to set task group for the new fair task
> in cgroup_post_fork().
>
> Since commit b1e8206582f9 ("sched: Fix yet more sched_fork() races")
> has already set task group for the new fair task in sched_cgroup_fork(),
> so cpu_cgrp_subsys->fork() can be removed.
>
> cgroup_can_fork() --> pin parent's sched_task_group
> sched_cgroup_fork()
> __set_task_cpu --> set task group
> cgroup_post_fork()
> ss->fork() := cpu_cgroup_fork() --> set again
>
> After this change, task_change_group_fair() only need to care about
> task cgroup migration, make the code much simplier.
>
> This patch move the task se depth setting to set_task_rq(), which
> is called when task moves across CPUs/groups, is a better place than
> attach_entity_cfs_rq(). The latter is also used when change task's
> sched_class, in which case the group/depth doesn't change actually.
>
The commit message needs some minor fixes but apart from this
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
> kernel/sched/core.c | 27 ++++-----------------------
> kernel/sched/fair.c | 31 +------------------------------
> kernel/sched/sched.h | 6 ++----
> 3 files changed, 7 insertions(+), 57 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c16f8cc5de08..f44bc5b889ab 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -481,8 +481,7 @@ sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
> * p->se.load, p->rt_priority,
> * p->dl.dl_{runtime, deadline, period, flags, bw, density}
> * - sched_setnuma(): p->numa_preferred_nid
> - * - sched_move_task()/
> - * cpu_cgroup_fork(): p->sched_task_group
> + * - sched_move_task(): p->sched_task_group
> * - uclamp_update_active() p->uclamp*
> *
> * p->state <- TASK_*:
> @@ -10098,7 +10097,7 @@ void sched_release_group(struct task_group *tg)
> spin_unlock_irqrestore(&task_group_lock, flags);
> }
>
> -static void sched_change_group(struct task_struct *tsk, int type)
> +static void sched_change_group(struct task_struct *tsk)
> {
> struct task_group *tg;
>
> @@ -10114,7 +10113,7 @@ static void sched_change_group(struct task_struct *tsk, int type)
>
> #ifdef CONFIG_FAIR_GROUP_SCHED
> if (tsk->sched_class->task_change_group)
> - tsk->sched_class->task_change_group(tsk, type);
> + tsk->sched_class->task_change_group(tsk);
> else
> #endif
> set_task_rq(tsk, task_cpu(tsk));
> @@ -10145,7 +10144,7 @@ void sched_move_task(struct task_struct *tsk)
> if (running)
> put_prev_task(rq, tsk);
>
> - sched_change_group(tsk, TASK_MOVE_GROUP);
> + sched_change_group(tsk);
>
> if (queued)
> enqueue_task(rq, tsk, queue_flags);
> @@ -10223,23 +10222,6 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
> sched_unregister_group(tg);
> }
>
> -/*
> - * This is called before wake_up_new_task(), therefore we really only
> - * have to set its group bits, all the other stuff does not apply.
> - */
> -static void cpu_cgroup_fork(struct task_struct *task)
> -{
> - struct rq_flags rf;
> - struct rq *rq;
> -
> - rq = task_rq_lock(task, &rf);
> -
> - update_rq_clock(rq);
> - sched_change_group(task, TASK_SET_GROUP);
> -
> - task_rq_unlock(rq, task, &rf);
> -}
> -
> static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
> {
> struct task_struct *task;
> @@ -11136,7 +11118,6 @@ struct cgroup_subsys cpu_cgrp_subsys = {
> .css_released = cpu_cgroup_css_released,
> .css_free = cpu_cgroup_css_free,
> .css_extra_stat_show = cpu_extra_stat_show,
> - .fork = cpu_cgroup_fork,
> .can_attach = cpu_cgroup_can_attach,
> .attach = cpu_cgroup_attach,
> .legacy_cftypes = cpu_legacy_files,
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8bed75757e65..fdb9125fe34e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -11325,14 +11325,6 @@ static void attach_entity_cfs_rq(struct sched_entity *se)
> {
> struct cfs_rq *cfs_rq = cfs_rq_of(se);
>
> -#ifdef CONFIG_FAIR_GROUP_SCHED
> - /*
> - * Since the real-depth could have been changed (only FAIR
> - * class maintain depth value), reset depth properly.
> - */
> - se->depth = se->parent ? se->parent->depth + 1 : 0;
> -#endif
> -
> /* Synchronize entity with its cfs_rq */
> update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
> attach_entity_load_avg(cfs_rq, se);
> @@ -11431,15 +11423,7 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
> }
>
> #ifdef CONFIG_FAIR_GROUP_SCHED
> -static void task_set_group_fair(struct task_struct *p)
> -{
> - struct sched_entity *se = &p->se;
> -
> - set_task_rq(p, task_cpu(p));
> - se->depth = se->parent ? se->parent->depth + 1 : 0;
> -}
> -
> -static void task_move_group_fair(struct task_struct *p)
> +static void task_change_group_fair(struct task_struct *p)
> {
> detach_task_cfs_rq(p);
> set_task_rq(p, task_cpu(p));
> @@ -11451,19 +11435,6 @@ static void task_move_group_fair(struct task_struct *p)
> attach_task_cfs_rq(p);
> }
>
> -static void task_change_group_fair(struct task_struct *p, int type)
> -{
> - switch (type) {
> - case TASK_SET_GROUP:
> - task_set_group_fair(p);
> - break;
> -
> - case TASK_MOVE_GROUP:
> - task_move_group_fair(p);
> - break;
> - }
> -}
> -
> void free_fair_sched_group(struct task_group *tg)
> {
> int i;
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 317480d535b0..8433e22da3ab 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1901,6 +1901,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
> set_task_rq_fair(&p->se, p->se.cfs_rq, tg->cfs_rq[cpu]);
> p->se.cfs_rq = tg->cfs_rq[cpu];
> p->se.parent = tg->se[cpu];
> + p->se.depth = tg->se[cpu] ? tg->se[cpu]->depth + 1 : 0;
> #endif
>
> #ifdef CONFIG_RT_GROUP_SCHED
> @@ -2163,11 +2164,8 @@ struct sched_class {
>
> void (*update_curr)(struct rq *rq);
>
> -#define TASK_SET_GROUP 0
> -#define TASK_MOVE_GROUP 1
> -
> #ifdef CONFIG_FAIR_GROUP_SCHED
> - void (*task_change_group)(struct task_struct *p, int type);
> + void (*task_change_group)(struct task_struct *p);
> #endif
> };
>
> --
> 2.36.1
>
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