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Tue, 07 Oct 2025 08:22:16 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20251006104402.946760805@infradead.org> <20251006104526.964100769@infradead.org> In-Reply-To: <20251006104526.964100769@infradead.org> From: Vincent Guittot Date: Tue, 7 Oct 2025 17:22:05 +0200 X-Gm-Features: AS18NWBp67oekCA5wJuqsWfMSlc_Mr63BTHm_H8SM2ppgSw678wieZ4yFPZoLog Message-ID: Subject: Re: [PATCH 04/12] sched: Cleanup sched_delayed handling for class switches To: Peter Zijlstra Cc: tj@kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org, juri.lelli@redhat.com, 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 Content-Type: text/plain; charset="UTF-8" On Mon, 6 Oct 2025 at 12:45, Peter Zijlstra wrote: > > Use the new sched_class::switching_from() method to dequeue delayed > tasks before switching to another class. > > Signed-off-by: Peter Zijlstra (Intel) > Acked-by: Tejun Heo Reviewed-by: Vincent Guittot > --- > kernel/sched/core.c | 12 ++++++++---- > kernel/sched/ext.c | 6 ------ > kernel/sched/fair.c | 7 +++++++ > kernel/sched/syscalls.c | 3 --- > 4 files changed, 15 insertions(+), 13 deletions(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7368,9 +7368,6 @@ void rt_mutex_setprio(struct task_struct > queue_flag &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE); > } > > - if (prev_class != next_class && p->se.sched_delayed) > - dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK); > - > scoped_guard (sched_change, p, queue_flag) { > /* > * Boosting condition are: > @@ -10845,8 +10842,15 @@ struct sched_change_ctx *sched_change_be > if (WARN_ON_ONCE(flags & (DEQUEUE_SAVE | DEQUEUE_MOVE))) > flags &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE); > > - if (p->sched_class->switching_from) > + if (p->sched_class->switching_from) { > + /* > + * switching_from_fair() assumes CLASS implies NOCLOCK; > + * fixing this assumption would mean switching_from() > + * would need to be able to change flags. > + */ > + WARN_ON(!(flags & DEQUEUE_NOCLOCK)); > p->sched_class->switching_from(rq, p); > + } > } > > *ctx = (struct sched_change_ctx){ > --- a/kernel/sched/ext.c > +++ b/kernel/sched/ext.c > @@ -3924,9 +3924,6 @@ static void scx_disable_workfn(struct kt > queue_flags &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE); > } > > - if (old_class != new_class && p->se.sched_delayed) > - dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK); > - > scoped_guard (sched_change, p, queue_flags) { > p->sched_class = new_class; > } > @@ -4677,9 +4674,6 @@ static int scx_enable(struct sched_ext_o > queue_flags &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE); > } > > - if (old_class != new_class && p->se.sched_delayed) > - dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK); > - > scoped_guard (sched_change, p, queue_flags) { > p->scx.slice = SCX_SLICE_DFL; > p->sched_class = new_class; > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -13237,6 +13237,12 @@ static void attach_task_cfs_rq(struct ta > attach_entity_cfs_rq(se); > } > > +static void switching_from_fair(struct rq *rq, struct task_struct *p) > +{ > + if (p->se.sched_delayed) > + dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK); > +} > + > static void switched_from_fair(struct rq *rq, struct task_struct *p) > { > detach_task_cfs_rq(p); > @@ -13638,6 +13644,7 @@ DEFINE_SCHED_CLASS(fair) = { > > .reweight_task = reweight_task_fair, > .prio_changed = prio_changed_fair, > + .switching_from = switching_from_fair, > .switched_from = switched_from_fair, > .switched_to = switched_to_fair, > > --- a/kernel/sched/syscalls.c > +++ b/kernel/sched/syscalls.c > @@ -689,9 +689,6 @@ int __sched_setscheduler(struct task_str > queue_flags &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE); > } > > - if (prev_class != next_class && p->se.sched_delayed) > - dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK); > - > scoped_guard (sched_change, p, queue_flags) { > > if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) { > >