From nobody Thu Sep 11 01:36:09 2025 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 05A6132C305; Wed, 10 Sep 2025 16:00:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757520043; cv=none; b=oWr4QOVkGTV9+stgcBCrMJ957HxwribNnWa0+qHKX+qgAg+/5s4Ak+xudDpWGKS+ea3Kx/jccu3pRw36GZciXUf5RGwTuxKA26al7CtBy64XbrIxwyORPEfvgcCSrmqc1dAK9GikduGv087Js3N7Bk36wQvyuxP0Omto+W2aQbg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757520043; c=relaxed/simple; bh=UabuqHs82eiB6wfw3nlkdJGIxKNkVMrU3JFOzGrGF74=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=Yr3Z7P32E6R0NNb7K9omYlvyQ/zl6cfX7f8t3iHUc067ScD7lhYiYIdhE7opyt1dE27elhrWXvmzT2fZVUxMAbZAJzA9oR3fCr4vgAkKvZZazlWLMioLBdn4W14dPu3y5KCbQExcjaR4P6Y5Kv1NXOlQJws82e4kPcHMyl76vgg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=kWw6DIei; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="kWw6DIei" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=noQZMFROCfJfcSZHYVFLL9z8ZG1W1SPyFqWShS69sJc=; b=kWw6DIeiTHMghlxf3k9tQVKS1a g9e5o2osRsvWF6CwSdr5T6XDVZ+gCsChyRFQdkrjuxBejosIj/50nnwT4yyANduSdGwWa34Q9FV2O I7+wB1/z9h2rUch8WICPfxkmDS9NKouMjrEbsKq24A+o5E5uIJ4bSnYvMh5DRPYUWbBpRbSlsmg+N jXnmMWFtj8qpkYz5leMk1WKv5XqSkg4dQXljX0mzfQguOqnb61oaH4SbGeONIGzUTvWzV11hox4lZ Q9hjh59z4O1muiPatnWf4Av/yvuWwGNU2h6WRomih5j4OIy2fWES6+dn34rIkuUyryHPfD2i97lN5 8xQDl29g==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwNFF-0000000BXot-3xc4; Wed, 10 Sep 2025 16:00:30 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 8318E302D9C; Wed, 10 Sep 2025 18:00:28 +0200 (CEST) Message-ID: <20250910155808.649485170@infradead.org> User-Agent: quilt/0.68 Date: Wed, 10 Sep 2025 17:44:12 +0200 From: Peter Zijlstra To: tj@kernel.org Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, longman@redhat.com, hannes@cmpxchg.org, mkoutny@suse.com, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, cgroups@vger.kernel.org, sched-ext@lists.linux.dev, liuwenfang@honor.com, tglx@linutronix.de Subject: [PATCH 03/14] sched: Fold sched_class::switch{ing,ed}_{to,from}() into the change pattern References: <20250910154409.446470175@infradead.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" Add {DE,EN}QUEUE_CLASS and fold the sched_class::switch* methods into the change pattern. This completes and makes the pattern more symmetric. This changes the order of callbacks slightly: | | switching_from() dequeue_task(); | dequeue_task() put_prev_task(); | put_prev_task() | switched_from() | ... change task ... | ... change task ... | switching_to(); | switching_to() enqueue_task(); | enqueue_task() set_next_task(); | set_next_task() prev_class->switched_from() | switched_to() | switched_to() | Notably, it moves the switched_from() callback right after the dequeue/put. Existing implementations don't appear to be affected by this change in location -- specifically the task isn't enqueued on the class in question in either location. Make (CLASS)^(SAVE|MOVE), because there is nothing to save-restore when changing scheduling classes. Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/core.c | 56 +++++++++++++++++++++---------------------= ----- kernel/sched/ext.c | 26 ++++++++++++++++----- kernel/sched/idle.c | 4 +-- kernel/sched/rt.c | 2 - kernel/sched/sched.h | 22 ++++++------------ kernel/sched/stop_task.c | 4 +-- kernel/sched/syscalls.c | 9 +++++-- 7 files changed, 66 insertions(+), 57 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2167,34 +2167,9 @@ inline int task_curr(const struct task_s return cpu_curr(task_cpu(p)) =3D=3D p; } =20 -/* - * ->switching_to() is called with the pi_lock and rq_lock held and must n= ot - * mess with locking. - */ -void check_class_changing(struct rq *rq, struct task_struct *p, - const struct sched_class *prev_class) +void check_prio_changed(struct rq *rq, struct task_struct *p, int oldprio) { - if (prev_class !=3D p->sched_class && p->sched_class->switching_to) - p->sched_class->switching_to(rq, p); -} - -/* - * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock, - * use the balance_callback list if you want balancing. - * - * this means any call to check_class_changed() must be followed by a call= to - * balance_callback(). - */ -void check_class_changed(struct rq *rq, struct task_struct *p, - const struct sched_class *prev_class, - int oldprio) -{ - if (prev_class !=3D p->sched_class) { - if (prev_class->switched_from) - prev_class->switched_from(rq, p); - - p->sched_class->switched_to(rq, p); - } else if (oldprio !=3D p->prio || dl_task(p)) + if (oldprio !=3D p->prio || dl_task(p)) p->sched_class->prio_changed(rq, p, oldprio); } =20 @@ -7423,6 +7398,11 @@ void rt_mutex_setprio(struct task_struct prev_class =3D p->sched_class; next_class =3D __setscheduler_class(p->policy, prio); =20 + if (prev_class !=3D next_class) { + queue_flag |=3D DEQUEUE_CLASS; + queue_flag &=3D ~(DEQUEUE_SAVE | DEQUEUE_MOVE); + } + if (prev_class !=3D next_class && p->se.sched_delayed) dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK); =20 @@ -7459,11 +7439,10 @@ void rt_mutex_setprio(struct task_struct =20 p->sched_class =3D next_class; p->prio =3D prio; - - check_class_changing(rq, p, prev_class); } =20 - check_class_changed(rq, p, prev_class, oldprio); + if (!(queue_flag & DEQUEUE_CLASS)) + check_prio_changed(rq, p, oldprio); out_unlock: /* Avoid rq from going away on us: */ preempt_disable(); @@ -10896,6 +10875,14 @@ struct sched_change_ctx *sched_change_be =20 lockdep_assert_rq_held(rq); =20 + if (flags & DEQUEUE_CLASS) { + if (WARN_ON_ONCE(flags & (DEQUEUE_SAVE | DEQUEUE_MOVE))) + flags &=3D ~(DEQUEUE_SAVE | DEQUEUE_MOVE); + + if (p->sched_class->switching_from) + p->sched_class->switching_from(rq, p); + } + *ctx =3D (struct sched_change_ctx){ .p =3D p, .flags =3D flags, @@ -10908,6 +10895,9 @@ struct sched_change_ctx *sched_change_be if (ctx->running) put_prev_task(rq, p); =20 + if ((flags & DEQUEUE_CLASS) && p->sched_class->switched_from) + p->sched_class->switched_from(rq, p); + return ctx; } =20 @@ -10918,8 +10908,14 @@ void sched_change_end(struct sched_chang =20 lockdep_assert_rq_held(rq); =20 + if ((ctx->flags & ENQUEUE_CLASS) && p->sched_class->switching_to) + p->sched_class->switching_to(rq, p); + if (ctx->queued) enqueue_task(rq, p, ctx->flags | ENQUEUE_NOCLOCK); if (ctx->running) set_next_task(rq, p); + + if ((ctx->flags & ENQUEUE_CLASS) && p->sched_class->switched_to) + p->sched_class->switched_to(rq, p); } --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -4999,21 +4999,28 @@ static void scx_disable_workfn(struct kt =20 scx_task_iter_start(&sti); while ((p =3D scx_task_iter_next_locked(&sti))) { + unsigned int queue_flags =3D DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLO= CK; const struct sched_class *old_class =3D p->sched_class; const struct sched_class *new_class =3D __setscheduler_class(p->policy, p->prio); =20 update_rq_clock(task_rq(p)); =20 + if (old_class !=3D new_class) { + queue_flags |=3D DEQUEUE_CLASS; + queue_flags &=3D ~(DEQUEUE_SAVE | DEQUEUE_MOVE); + } + if (old_class !=3D new_class && p->se.sched_delayed) dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_N= OCLOCK); =20 - scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOC= LOCK) { + scoped_guard (sched_change, p, queue_flags) { p->sched_class =3D new_class; - check_class_changing(task_rq(p), p, old_class); } =20 - check_class_changed(task_rq(p), p, old_class, p->prio); + if (!(queue_flags & DEQUEUE_CLASS)) + check_prio_changed(task_rq(p), p, p->prio); + scx_exit_task(p); } scx_task_iter_stop(&sti); @@ -5742,6 +5749,7 @@ static int scx_enable(struct sched_ext_o percpu_down_write(&scx_fork_rwsem); scx_task_iter_start(&sti); while ((p =3D scx_task_iter_next_locked(&sti))) { + unsigned int queue_flags =3D DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLO= CK; const struct sched_class *old_class =3D p->sched_class; const struct sched_class *new_class =3D __setscheduler_class(p->policy, p->prio); @@ -5751,16 +5759,22 @@ static int scx_enable(struct sched_ext_o =20 update_rq_clock(task_rq(p)); =20 + if (old_class !=3D new_class) { + queue_flags |=3D DEQUEUE_CLASS; + queue_flags &=3D ~(DEQUEUE_SAVE | DEQUEUE_MOVE); + } + if (old_class !=3D new_class && p->se.sched_delayed) dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_N= OCLOCK); =20 - scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOC= LOCK) { + scoped_guard (sched_change, p, queue_flags) { p->scx.slice =3D SCX_SLICE_DFL; p->sched_class =3D new_class; - check_class_changing(task_rq(p), p, old_class); } =20 - check_class_changed(task_rq(p), p, old_class, p->prio); + if (!(queue_flags & DEQUEUE_CLASS)) + check_prio_changed(task_rq(p), p, p->prio); + put_task_struct(p); } scx_task_iter_stop(&sti); --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -498,7 +498,7 @@ static void task_tick_idle(struct rq *rq { } =20 -static void switched_to_idle(struct rq *rq, struct task_struct *p) +static void switching_to_idle(struct rq *rq, struct task_struct *p) { BUG(); } @@ -536,6 +536,6 @@ DEFINE_SCHED_CLASS(idle) =3D { .task_tick =3D task_tick_idle, =20 .prio_changed =3D prio_changed_idle, - .switched_to =3D switched_to_idle, + .switching_to =3D switching_to_idle, .update_curr =3D update_curr_idle, }; --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2589,8 +2589,8 @@ DEFINE_SCHED_CLASS(rt) =3D { =20 .get_rr_interval =3D get_rr_interval_rt, =20 - .prio_changed =3D prio_changed_rt, .switched_to =3D switched_to_rt, + .prio_changed =3D prio_changed_rt, =20 .update_curr =3D update_curr_rt, =20 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -20,7 +20,6 @@ #include #include #include - #include #include #include @@ -2344,6 +2343,7 @@ extern const u32 sched_prio_to_wmult[40 =20 #define DEQUEUE_MIGRATING 0x0010 /* Matches ENQUEUE_MIGRATING */ #define DEQUEUE_DELAYED 0x0020 /* Matches ENQUEUE_DELAYED */ +#define DEQUEUE_CLASS 0x0040 /* Matches ENQUEUE_CLASS */ =20 #define DEQUEUE_SPECIAL 0x00010000 #define DEQUEUE_THROTTLE 0x00020000 @@ -2355,6 +2355,7 @@ extern const u32 sched_prio_to_wmult[40 =20 #define ENQUEUE_MIGRATING 0x0010 #define ENQUEUE_DELAYED 0x0020 +#define ENQUEUE_CLASS 0x0040 =20 #define ENQUEUE_HEAD 0x00010000 #define ENQUEUE_REPLENISH 0x00020000 @@ -2418,14 +2419,11 @@ struct sched_class { void (*task_fork)(struct task_struct *p); void (*task_dead)(struct task_struct *p); =20 - /* - * The switched_from() call is allowed to drop rq->lock, therefore we - * cannot assume the switched_from/switched_to pair is serialized by - * rq->lock. They are however serialized by p->pi_lock. - */ - void (*switching_to) (struct rq *this_rq, struct task_struct *task); - void (*switched_from)(struct rq *this_rq, struct task_struct *task); - void (*switched_to) (struct rq *this_rq, struct task_struct *task); + void (*switching_from)(struct rq *this_rq, struct task_struct *task); + void (*switched_from) (struct rq *this_rq, struct task_struct *task); + void (*switching_to) (struct rq *this_rq, struct task_struct *task); + void (*switched_to) (struct rq *this_rq, struct task_struct *task); + void (*reweight_task)(struct rq *this_rq, struct task_struct *task, const struct load_weight *lw); void (*prio_changed) (struct rq *this_rq, struct task_struct *task, @@ -3854,11 +3852,7 @@ extern void set_load_weight(struct task_ extern void enqueue_task(struct rq *rq, struct task_struct *p, int flags); extern bool dequeue_task(struct rq *rq, struct task_struct *p, int flags); =20 -extern void check_class_changing(struct rq *rq, struct task_struct *p, - const struct sched_class *prev_class); -extern void check_class_changed(struct rq *rq, struct task_struct *p, - const struct sched_class *prev_class, - int oldprio); +extern void check_prio_changed(struct rq *rq, struct task_struct *p, int o= ldprio); =20 extern struct balance_callback *splice_balance_callbacks(struct rq *rq); extern void balance_callbacks(struct rq *rq, struct balance_callback *head= ); --- a/kernel/sched/stop_task.c +++ b/kernel/sched/stop_task.c @@ -75,7 +75,7 @@ static void task_tick_stop(struct rq *rq { } =20 -static void switched_to_stop(struct rq *rq, struct task_struct *p) +static void switching_to_stop(struct rq *rq, struct task_struct *p) { BUG(); /* its impossible to change to this class */ } @@ -112,6 +112,6 @@ DEFINE_SCHED_CLASS(stop) =3D { .task_tick =3D task_tick_stop, =20 .prio_changed =3D prio_changed_stop, - .switched_to =3D switched_to_stop, + .switching_to =3D switching_to_stop, .update_curr =3D update_curr_stop, }; --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -684,6 +684,11 @@ int __sched_setscheduler(struct task_str prev_class =3D p->sched_class; next_class =3D __setscheduler_class(policy, newprio); =20 + if (prev_class !=3D next_class) { + queue_flags |=3D DEQUEUE_CLASS; + queue_flags &=3D ~(DEQUEUE_SAVE | DEQUEUE_MOVE); + } + if (prev_class !=3D next_class && p->se.sched_delayed) dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK); =20 @@ -695,7 +700,6 @@ int __sched_setscheduler(struct task_str p->prio =3D newprio; } __setscheduler_uclamp(p, attr); - check_class_changing(rq, p, prev_class); =20 if (scope->queued) { /* @@ -707,7 +711,8 @@ int __sched_setscheduler(struct task_str } } =20 - check_class_changed(rq, p, prev_class, oldprio); + if (!(queue_flags & DEQUEUE_CLASS)) + check_prio_changed(rq, p, oldprio); =20 /* Avoid rq from going away on us: */ preempt_disable();