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 DAE8544E055; Wed, 30 Sep 2026 08:11:38 +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=1790755904; cv=none; b=afmKHM3B+O92utvLp/37p6Is9OcAmwIhHc6W/ZPdV6OSHhPIn6r3oe5+TrmWkrsRZXp9L85KwlS4zR0ar3Nzu5P5e5SgFvJhQ7ORi17vgcABgJSyS2Y2GX+DeIahiVDuhhqqKFNvaYwywzdjZ5rgwdVIDHTaCXDXwMA1OSc29a8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790755904; c=relaxed/simple; bh=n6LqOCOL05LpmXLjZqV2F6/Qv/JfqGYo6fy5jnfWq9E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WfO+XjFUGiV7Q39+YKcC5l//+c85FZlBifs1nizzemk8VHpz84seTJgDvxs/IWYGAd+zHHQzNPLK0uvBK92BklgGJxHPBVM76AQ8cSdCRPkUGQIXrOkMdVifogMclzKje/BBzjioNkMH8zPKS1Uwp71zHv/p5i2t09xzq/7SQLc= 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=Nw2M0uL1; 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="Nw2M0uL1" 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=n6LqOCOL05LpmXLjZqV2F6/Qv/JfqGYo6fy5jnfWq9E=; b=Nw2M0uL14wIlEsHYUYs6yOzm3j +dKb5C0Kk3YlSidiL0Ba6JIcuRbWgH5asWlAeQ6RCIgUTxc8oiYwiaW9pTy1YcjraqGOvNuLBHXrR o6hn63cIpymrVnr+g8y2G3DqDw/KecId2PjM7AdgZpUfR5cMKrxcl+ElFJk6DeoSaXvarakfuClBG YUcAa5vqwPJiKioSUMjpt7VInDRpT/eTyDtuCJbY8saKmkBDjg9R/pkGHuEeyyQRGAmJTC7023SEp jLgLIIH8diWHICjaA6J7xsH8JAQC+ZoUOPBCRIWTUGyGPSuAfv/Z09DwpiGj9al/luT4ysuuPEirh s3odEgwg==; 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 1xBpPT-00000003Vu7-3kBu; Wed, 30 Sep 2026 08:11:28 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id B93F4300673; Wed, 30 Sep 2026 10:11:25 +0200 (CEST) Date: Wed, 30 Sep 2026 10:11:25 +0200 From: Peter Zijlstra To: Waiman Long Cc: Andrea Righi , Michal =?iso-8859-1?Q?Koutn=FD?= , Tejun Heo , David Vernet , Changwoo Min , Ridong Chen , Johannes Weiner , sched-ext@lists.linux.dev, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] cgroup/cpuset: Protect is_in_v2_mode() in cpuset_num_cpus() Message-ID: <20260930081125.GF88198@noisy.programming.kicks-ass.net> References: <20260929084124.626693-1-arighi@nvidia.com> <20260929084124.626693-2-arighi@nvidia.com> <20260929-making-language-254d9c6a6605@there> <20260929190853.GE88198@noisy.programming.kicks-ass.net> <500cb19a-549b-4055-a807-c3c40da787ae@redhat.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: <500cb19a-549b-4055-a807-c3c40da787ae@redhat.com> On Tue, Sep 29, 2026 at 03:46:23PM -0400, Waiman Long wrote: > The cpuset_v2_mode mount option is only for making the cpuset.cpus and > cpuset.mems behave like in v2. The cpu-cgroup and cpuset-cgroup can still be > in separate hierarchies. If cross-cgroup transition is the main point, it > won't work with the cpuset_v2_mode mount option. We should switch to use > cpuset_v2(). Yes, the cross-cgroup transition is fundamental to how this works. Without that you cannot reasonably talk about the CPUs of a cpu-cgroup, you need to have cpu and cpuset aligned.