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 BE8AB3769E9; Mon, 10 Aug 2026 07:38:51 +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=1786347537; cv=none; b=BXciAJtRZGBkZJswTtaESbJVifyeAro/LOg5Vb+3avP+WSuStSW5gM3a+BGu/5D5oeaj/uSps3IqHAckTqh5zBXHHuNOerqBgZN73ki6ljIR2slOvSJKNQ0eD9UrqeO+Z9M1TYY2zfJwAlQBPNt6SPcGLEgmlkVnImnT8xfauoM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786347537; c=relaxed/simple; bh=Tz0ZCRWFixHAIs7oZ5wtKehSDPy2ZEjcQK/B9l4XAfU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=RLnoISF7R0LZVjR76uUGXknio+xxnH9PRO/DqndUUdp3WiKnRjAogtVUt7ta78Ynk+g3/BBu4LQNmw5/FUgOLwwQUPVbiDqSq6qhotso3+hbq/XLd8ehg7M6kpJCfSiFQc9YK5RoLoiqvH44MgI2wwXRkrHFhafpssSH+GFBZyM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=dzA5GGQQ; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass 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="dzA5GGQQ" 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=pZhZEbnFi3CBwXPlZfbRBsBUWJjVwpj8fu0LSjowEHI=; b=dzA5GGQQxlhvt0A3xsvHTclJoZ hE6NWGkHTXRl+7riYaY09G2gxc9E+g58Hck7Lwkki2fjfezYjL4VGNTHvTC/ob32U3Ui/kkozynEK rKOcXkZBLN/up5wKpsfmgbcSneX/0zkSx5c50SPX/DIhu+GwNCHKrfGaHWMovGrNS3HmxvupQqbQE CBXOrrJqId96TW57+0GtsxBjPTNHSPfIzH00nwFXYEDcC2WqJ+fElFpLf+NsNSyiYraRWies7CxJs PAu3eczVhQZ1ZHS2sHmu+Qfab8bAEooypK8YFRZlm6vKCztwzn3VYXFNAHlmMYlndovg4HpFmjuj5 dKYGoiyw==; 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 4.99.2 #2 (Red Hat Linux)) id 1wtKaf-0000000Db7n-2oex; Mon, 10 Aug 2026 07:38:34 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 9A55A3030A6; Mon, 10 Aug 2026 09:38:30 +0200 (CEST) Date: Mon, 10 Aug 2026 09:38:30 +0200 From: Peter Zijlstra To: Jose Fernandez Cc: John Stultz , stable@vger.kernel.org, linux-kernel@vger.kernel.org, Sasha Levin , Janne Huttunen , Zicheng Qu , Vincent Guittot , K Prateek Nayak , Shubhang Kaushik , Dietmar Eggemann , Xuewen Yan , William Montaz Subject: Re: [PATCH 6.18] sched/fair: Revert 6d71a9c61604 ("sched/fair: Fix EEVDF entity placement bug causing scheduling lag") Message-ID: <20260810073830.GC1642880@noisy.programming.kicks-ass.net> References: <20260324100126.3502-1-willymontaz@gmail.com> <20260415211149.2658910-1-jstultz@google.com> 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: On Mon, Aug 10, 2026 at 01:44:25AM +0000, Jose Fernandez wrote: > On Wed, Apr 15, 2026 at 09:10:53PM +0000, John Stultz wrote: > > From: Peter Zijlstra > > > > [ Upstream commit 101f3498b4bdfef97152a444847948de1543f692 ] > > > [...] > > (cherry picked from commit 101f3498b4bdfef97152a444847948de1543f692) > > [jstultz: Resolved minor collision in the revert against 6.18-stable] > > Signed-off-by: John Stultz > > We have been hitting this on 6.18.y in production. The setup is a > thread spinning on one CPU inside a cgroup that holds nearly all the > weight on that CPU. That cgroup's weight gets recalculated on almost > every tick, and the per-cpu kworker on the same CPU ends up runnable > but never picked for minutes to hours. We see it as workqueue lockup > reports and hung tasks stuck behind lru_add_drain_all(). > > I tested this patch on 6.18.44 in a 4 vCPU KVM guest with a reproducer > along the lines of William's script. Three spinners are pinned to three > CPUs inside a nested cgroup with a high cpu.weight, and some extra load > in the group keeps its weight changing. On plain 6.18.44 the kworkers > on those CPUs get stuck runnable but never picked, and their vruntime > stops moving. With this patch they run normally. Running the same load > with no cgroup does not starve anything on either kernel. > > Peter said in April that this could go to 6.18 [1]. Janne Huttunen > posted the same backport last month [2] and Sasha is holding it for > Peter's ack on taking the revert without 4823725d9d1d [3]. This patch > and [2] differ only in div64_long() against div_s64(). > > Tested-by: Jose Fernandez (Anthropic) > > [1] https://lore.kernel.org/all/20260407134519.GH3738010@noisy.programming.kicks-ass.net/ > [2] https://lore.kernel.org/stable/PAWPR07MB100712177EB29A65F4385E4C29ACF2@PAWPR07MB10071.eurprd07.prod.outlook.com/ > [3] https://lore.kernel.org/stable/20260725192000.stable-0001@kernel.org/ Yeah, this should be fine without 4823725d9d1d.