From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 7CD9E2459F3; Thu, 9 Oct 2025 14:09:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760018989; cv=none; b=U0uRqSshhajsHXDSlKB3n6PMTYMb1TXUD7F4l/OZ08ASpotuNeze7ux23GnYtoHxcrC0dqRXijBcYIJKytIHm+ZT4V7cl4eKFHXkbZ0BF98Yv5g0EP1NfnfdtQcnBzeYf5IEei+tN0Nqg5osZZTBwd1zcLsHRV042JK4Nrc0UHM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760018989; c=relaxed/simple; bh=tDJS4NRxkFnQkEwxcMTkDM1sNOfGQ40YA+cT0EfHN1A=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ChZNtNWaLWot4OpX66Q0h0JpQJquQI1MeHPIhnf6Tx6bX10xFOqH/cAs3f1WWyURwvszUU2EgK8NNZ8grcro8UDMeKXhKiv1M4fL9HtPYv9RAXEibFPTiWoBHco42f4q7yNO5Cys+ewxC/bcQo4cF0IE8YEmFGl0JRgvIWF7yqw= 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=nAXgoFtI; arc=none smtp.client-ip=90.155.92.199 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="nAXgoFtI" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ieBvCbBheNPFtBxoISVqmiEkRKqIWXh/v+HP5ZowhjI=; b=nAXgoFtIs28drwEauJTWwJGMeN R0382zPEDZu8KViUA23YGsIcqITo7rULbxEHggZb8TyUIJlbdiEuFkfBrBCdqb9kr9cC0tnmoisYt tlJpmN+kuzbwUrs3AhlYo0yAUF1RAuEC1/Mo4tbe06lTGX3puqiIglGdZOAQU/EVATkJzyyqfGs6W J1Nun6SJdCTW9mEqQpiIb7wEpdiDMCJ0Uus1ASFS3lg5jEAswzuAVbc/5mNbqQIeWKUPKFhiN94GG UhaxTi6qdVfzD0Yf9YL8tJoC0ZzLrNF5mhYcQel1+gwpwTy0sKAOCoYMaPri4zW1cbdP5jlxeu2Yq jk741fVA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1v6rKg-00000001Ubm-3AbJ; Thu, 09 Oct 2025 14:09:27 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id B1BDB300399; Thu, 09 Oct 2025 16:09:25 +0200 (CEST) Date: Thu, 9 Oct 2025 16:09:25 +0200 From: Peter Zijlstra To: Dietmar Eggemann Cc: tj@kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, 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: Re: [PATCH 03/12] sched: Fold sched_class::switch{ing,ed}_{to,from}() into the change pattern Message-ID: <20251009140925.GD4068168@noisy.programming.kicks-ass.net> References: <20251006104402.946760805@infradead.org> <20251006104526.861755244@infradead.org> <02452879-8998-47e0-9679-d2ff00503901@arm.com> <20251009135408.GD4067720@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: cgroups@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: <20251009135408.GD4067720@noisy.programming.kicks-ass.net> On Thu, Oct 09, 2025 at 03:54:08PM +0200, Peter Zijlstra wrote: > On Thu, Oct 09, 2025 at 03:30:02PM +0200, Dietmar Eggemann wrote: > > On 06.10.25 12:44, Peter Zijlstra wrote: > > > 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. > > > > This one causes a DL bw related warning when I run a simple 1 DL task > > rt-app workload: > > > Not sure yet how this is related to switched_from_dl() being now called earlier? > > Ooh, I might see a problem. task_non_contending() uses dl_task(), which > uses p->prio. The move above means it is now called using the 'old' > prio, whereas it used to run with the 'new' prio. > > Let me see if I can figure out something for this. Does this help? /me goes find rt-app. diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 615411a0a881..fe2272c812b2 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -405,7 +405,7 @@ static void __dl_clear_params(struct sched_dl_entity *dl_se); * up, and checks if the task is still in the "ACTIVE non contending" * state or not (in the second case, it updates running_bw). */ -static void task_non_contending(struct sched_dl_entity *dl_se) +static void task_non_contending(struct sched_dl_entity *dl_se, bool dl_task) { struct hrtimer *timer = &dl_se->inactive_timer; struct rq *rq = rq_of_dl_se(dl_se); @@ -444,10 +444,10 @@ static void task_non_contending(struct sched_dl_entity *dl_se) } else { struct task_struct *p = dl_task_of(dl_se); - if (dl_task(p)) + if (dl_task) sub_running_bw(dl_se, dl_rq); - if (!dl_task(p) || READ_ONCE(p->__state) == TASK_DEAD) { + if (!dl_task || READ_ONCE(p->__state) == TASK_DEAD) { struct dl_bw *dl_b = dl_bw_of(task_cpu(p)); if (READ_ONCE(p->__state) == TASK_DEAD) @@ -2045,7 +2045,7 @@ static void dequeue_dl_entity(struct sched_dl_entity *dl_se, int flags) * or "inactive") */ if (flags & DEQUEUE_SLEEP) - task_non_contending(dl_se); + task_non_contending(dl_se, true); } static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags) @@ -2970,7 +2970,7 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p) * will reset the task parameters. */ if (task_on_rq_queued(p) && p->dl.dl_runtime) - task_non_contending(&p->dl); + task_non_contending(&p->dl, false); /* * In case a task is setscheduled out from SCHED_DEADLINE we need to