From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.221.41 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793956274; b=U/hV5AxHWchuYKjoAqe9Qxjgrtzpo+i3a1OuoFbPlOuLChGADXaYz3VYCrAIj3ClWnWE oFPOhtEuqo3mU/yfbBynrF2ka2K1UoLDq5AwzYqkc20Lxuk5zRcJs/wlWHC7RzjdKavOg NIHWGmosnftVKM7OGHUsfD01Tw2MXtnxre30lN5bdRjgV7bOB0EVgf8AAHsMDoEGhBHRR O5coFAaGiMv9he1UMPHyOyuT2Eh21JCE1PcRl6gyG9MLkneJ/Orld6Wp8Syff3/M3tXOe aTUAvB19TEmhMG30zHGRB6jPFzo6baJTgj6Uuv9OrbYOLLFxpAspIgKgLAzo12Js6nw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793956274; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; bh=DmRVXXUsKTCET9way0Yyh49KlPqz6BX60Iow0coDuro=; b=RII7y2aPW7GLk7D0JwjJR/LIMfflox+pt+7RAZFQlhkJOXKs+lM8mhBFWldkER6wDoTM ZPrRwgrfYQjqmOMcHLdFJfrqVeTXKTdlCFcmVH3yfbnmcUJRNft3jF1/U7dYCbpDnP3Fv UlLs1rE/xhKBhk9IGGH7wLgqgK+io6fNOGskEv+ZpVxOpBjD6od6Fgx1s5IEnJByI8NmK HAcrk1wmVFIwYGPkETfsmGLIL/+CZntrofJcoyKv1PzgM7vKXyDy5iqtyR2QO9KKJrGOL 0HrBBG4Qa62Vv8zC9L6k+jJav/R3x/dWRUIiFDVhrnRbgG7p8VKVBxh7v/Aj7QMeGaQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=mRu0Q6qT; arc=none smtp.remote-ip=209.85.221.41 Received: from mail-wr1-f41.google.com (mail-wr1-f41.google.com [209.85.221.41]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 86EC0606A328 for ; Fri, 6 Nov 2026 09:11:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 86EC0606A328 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=mRu0Q6qT Received: by mail-wr1-f41.google.com with SMTP id ffacd0b85a97d-49061a82da0so22252f8f.3 for ; Fri, 06 Nov 2026 01:11:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1793956273; x=1794561073; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=DmRVXXUsKTCET9way0Yyh49KlPqz6BX60Iow0coDuro=; b=mRu0Q6qT8mR4QOqcCutNNrSj6LtEbSOfGjSJrHDqO0fo8HZPJYkPfkWQVIqjCJF7tA mf4e5llAPV3YsaYL2Yj41djUQS/S+EFwfwg0fo4gd85qihzgbiZpMzskOkD1v8nZZAtG kzr5Konj5ZDMrcyB3dzAFrBQ2SG827nytF4YIrLuJJLLwzoXvVlJDd7nOIT0hrGaTxcU +f581gVzGlACkzWxYX1eHyp4f1gFzJ1BzKGFtHGhXu8iRsPkRhEjK7nHy8z/KkSeNzJx m6LVhe2p95f2YgcfFA3mXJqxHItKRdQz2h/b5YRnwNHGlJJuz+okyxyblr/A5aEWRsIw 6WVw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793956273; x=1794561073; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=DmRVXXUsKTCET9way0Yyh49KlPqz6BX60Iow0coDuro=; b=GruivD7AcG27qR1KcmPyWMg7fivI36mH9mdQfQtjSDtZeNJq9yBzOR7jSkX1x1j3kg 0kwmlLZ+uCMzXIxa/Fm+Sgu06iV82lMmiOcMBe5bJJNVXJVA1p4rBUw+Pnk7Pg84tztc 5GlPrSad37oXVM42Ww1CKc/xZj/I+0gwTruzILSFzFmKR4bPICbnve8y50xykZ2tlvl1 tW3AjP1kGBMDmu7246WZj2yH0agi1u8/89KqNJXeA2sZ0tFbFv5UTf+WZlK+IEP3jK+T QQakszsaJrupbMuDBSceGc1dryCYV3c4BdRMgR3l2PSVvcI7q9WYpnuoimktPHIC/lGT oAng== X-Forwarded-Encrypted: i=1; AL+hErG3/bBex0sWwoB0Xmc/yQfccSJD8k48PobUOl6MVk5zf3pMj39GEKtFiY+f8KgYqde7kdEc8/BDmpMQmWs=@vger.kernel.org X-Gm-Message-State: APuU4Z/ON5Vhotg1GCuKyKOzNz14X0Eh6UjN2jAvJwFFSpNZw2w237cn v5A2KBs15OKMqskvaz7HuI1kJV+bgLSAAA6JZflXpw3KnJvciHZeCnUj X-Gm-Gg: AYBFou2r7XmmiPWr4BlOQr4mgg92HkqKsQfNJR7etVp0s/0VUfExU2llmQq1DnlDuSw HpteqoawlqKyAiFLx+vqgWTmLOpKelg50t3HQrhkH5hqUZHOoOztBQ4hXUjAN8PUl4/psKe7bKP l3PP2lx4CSf7WzueXwhLtwwh9V3s0WgL4RSxTveJylnepCNrr99j6IacnlNuJmA9XSlBxfljI56 CqQzGqDXqb61Wtip7OdwYbiY3WBTGKpPCXJKn94aul5aZQVeQCiQuMSaE75lg1Tm4PmhaO47Tz2 rKJ1FrsHBfy2H7fDYgj7xstEEsgKtdla9f4Xw6ZD+2p0frlcjTt7juz1neNhHRtVUv4rKZV8jeb KERMYr30vbNPh6ChPuGsaAHhatnm65k0xHTe3kq0WGAmA0j2vEhos19yI2gLcpMKknwCBKy3BIS 2H8Ljikvj1AMo8zoiaf/JrYA1JlGx+XBAS4TYh5SEjS9QdvLRJ0XxFP1OF41Tuxxg+6WqtbaavD aAcib9DbdOMc2gNTbFhDxMiC0IEtkNj11+cs34Hai7aAWinpbC+GLWHT4uNE9vGP5IxyaV7sqIn Jdnbv7ZqcEkT5ZOgBQh0vGzT237VT03gp4KNt37JcIZscFvb6AkvklSA X-Received: by 2002:a05:6000:288e:b0:48e:5d5e:c27b with SMTP id ffacd0b85a97d-492791c9108mr5062886f8f.6.1793956272726; Fri, 06 Nov 2026 01:11:12 -0800 (PST) Received: from scheduler.schedules ([85.100.66.184]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-492d723320csm2332431f8f.26.2026.11.06.01.11.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2026 01:11:12 -0800 (PST) Date: Fri, 6 Nov 2026 12:11:09 +0300 From: Kayra Cizmeci To: Peter Zijlstra Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, joshdon@google.com, tj@kernel.org, jakub@okonski.org Subject: Re: [PATCH 2/3] sched/fair: Make cfs_rq::idle the sum of ancestor tg::idle Message-ID: References: <20261105165525.011876858@infradead.org> <20261105170157.616859418@infradead.org> <20261106083106.GC1779021@noisy.programming.kicks-ass.net> <20261106090153.GD1779021@noisy.programming.kicks-ass.net> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20261106090153.GD1779021@noisy.programming.kicks-ass.net> On Fri, Nov 06, 2026 at 10:01:53AM +0100, Peter Zijlstra wrote: > On Fri, Nov 06, 2026 at 11:57:03AM +0300, Kayra Cizmeci wrote: > > On Fri, Nov 06, 2026 at 09:31:06AM +0100, Peter Zijlstra wrote: > > > On Thu, Nov 05, 2026 at 10:20:00PM +0300, Kayra Cizmeci wrote: > > > > On Thu, Nov 05, 2026 at 05:55:27PM +0100, Peter Zijlstra wrote: > > > > > Rather than keeping cfs_rq::idle as a copy of tg::idle, make it the sum of > > > > > all ancestor tg::idle. This makes it trivial to tell if the current cgroup > > > > > is marked idle somewhere along its ancestral path. > > > > > > > > > > This makes se_id_idle() behave differently. Notably is will now be true > > > > > when there is a idle cgroup anywhere in the ancestor path. This > > > > > addresses an issue where preemption of cgroup::idle was overlooked when > > > > > flattening the runqueue. > > > > > > > > How? The diff doesn't touches se_is_idle(). se_is_idle() just looks to > > > > the policy for tasks: > > > > > > > > static int se_is_idle(struct sched_entity *se) > > > > { > > > > if (entity_is_task(se)) > > > > return task_has_idle_policy(task_of(se)); > > > > return cfs_rq_is_idle(group_cfs_rq(se)); > > > > } > > > > > > > Or am I getting something wrong? > > > > > > cfs_rq_is_idle() := cfs_rq->idle > 0 > > > > > > and cfs_rq->idle is now getting incremented for the whole subtree. So if > > > any ancestor is idle, this is now true. > > > > > > Yeah, it is for group path. But we call se_is_idle for tasks in > > wakeup_preempt_fair(). Not groups, no? > > Ah, that's what you meant. So we should do something like: > > if (entity_is_task(se)) > return task_has_idle_policy(task_of(se)) || cfs_rq_is_idle(cfs_rq_of(se)); > return cfs_rq_is_idle(group_cfs_rq(se)); > > > no? > Yeah. AFAICT this should do the magic. BTW there was an issue about set_next_buddy() because of this I *think*. A task in a idle group could still be picked for buddy, but this change fixes that too. Cheers, Kayra