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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1t8gnc-00000004gfd-11cB; Wed, 06 Nov 2024 14:14:21 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 7BBD9300478; Wed, 6 Nov 2024 15:14:20 +0100 (CET) Date: Wed, 6 Nov 2024 15:14:20 +0100 From: Peter Zijlstra To: Mike Galbraith Cc: Phil Auld , 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, linux-kernel@vger.kernel.org, kprateek.nayak@amd.com, wuyun.abel@bytedance.com, youssefesmat@chromium.org, tglx@linutronix.de Subject: Re: [PATCH 17/24] sched/fair: Implement delayed dequeue Message-ID: <20241106141420.GZ33184@noisy.programming.kicks-ass.net> References: <20241101125659.GY14555@noisy.programming.kicks-ass.net> <20241101133822.GC689589@pauld.westford.csb> <20241101142649.GX9767@noisy.programming.kicks-ass.net> <20241101144225.GD689589@pauld.westford.csb> <20241101200704.GE689589@pauld.westford.csb> <59355fae66255a92f2cbc4d7ed38368ff3565140.camel@gmx.de> <20241104130515.GB749675@pauld.westford.csb> <1bffa5f2ca0fec8a00f84ffab86dc6e8408af31c.camel@gmx.de> <20241106135346.GL24862@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241106135346.GL24862@noisy.programming.kicks-ass.net> On Wed, Nov 06, 2024 at 02:53:46PM +0100, Peter Zijlstra wrote: > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 54d82c21fc8e..b083c6385e88 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3774,28 +3774,38 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags, > */ > static int ttwu_runnable(struct task_struct *p, int wake_flags) > { > + CLASS(__task_rq_lock, rq_guard)(p); > + struct rq *rq = rq_guard.rq; > > + if (!task_on_rq_queued(p)) > + return 0; > + > + update_rq_clock(rq); > + if (p->se.sched_delayed) { > + int queue_flags = ENQUEUE_DELAYED | ENQUEUE_NOCLOCK; > + > + /* > + * Since sched_delayed means we cannot be current anywhere, > + * dequeue it here and have it fall through to the > + * select_task_rq() case further along the ttwu() path. > + */ > + if (rq->nr_running > 1 && p->nr_cpus_allowed > 1) { > + dequeue_task(rq, p, DEQUEUE_SLEEP | queue_flags); > + return 0; > } > + > + enqueue_task(rq, p, queue_flags); And then I wondered... this means that !task_on_cpu() is true for sched_delayed, and thus we can move this in the below branch. But also, we can probably dequeue every such task, not only sched_delayed ones. > } > + if (!task_on_cpu(rq, p)) { > + /* > + * When on_rq && !on_cpu the task is preempted, see if > + * it should preempt the task that is current now. > + */ > + wakeup_preempt(rq, p, wake_flags); > + } > + ttwu_do_wakeup(p); > > + return 1; > } Yielding something like this on top... which boots. But since I forgot to make it a feature, I can't actually tell at this point.. *sigh* Anyway, more toys to poke at I suppose. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b083c6385e88..69b19ba77598 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3781,28 +3781,32 @@ static int ttwu_runnable(struct task_struct *p, int wake_flags) return 0; update_rq_clock(rq); - if (p->se.sched_delayed) { - int queue_flags = ENQUEUE_DELAYED | ENQUEUE_NOCLOCK; + if (!task_on_cpu(rq, p)) { + int queue_flags = DEQUEUE_NOCLOCK; + + if (p->se.sched_delayed) + queue_flags |= DEQUEUE_DELAYED; /* - * Since sched_delayed means we cannot be current anywhere, - * dequeue it here and have it fall through to the - * select_task_rq() case further along the ttwu() path. + * Since we're not current anywhere *AND* hold pi_lock, dequeue + * it here and have it fall through to the select_task_rq() + * case further along the ttwu() path. */ if (rq->nr_running > 1 && p->nr_cpus_allowed > 1) { dequeue_task(rq, p, DEQUEUE_SLEEP | queue_flags); return 0; } - enqueue_task(rq, p, queue_flags); - } - if (!task_on_cpu(rq, p)) { + if (p->se.sched_delayed) + enqueue_task(rq, p, queue_flags); + /* * When on_rq && !on_cpu the task is preempted, see if * it should preempt the task that is current now. */ wakeup_preempt(rq, p, wake_flags); } + SCHED_WARN_ON(p->se.sched_delayed); ttwu_do_wakeup(p); return 1;