From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B10D338B7DB; Thu, 22 Jan 2026 11:29:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769081360; cv=none; b=mw2El3BDgpzay2O2o+mYTcfAPhXFy9fjHfwIoP+cg9nY5eXckIFzRv9wQxzUOr3JduWxdle0s3EKFev6yUiuVctwKZ611fZ7WImQ5/HhwBUPEmyEq/3gsD1w0SXztXfWx6GgpHgZ1Awjtko8sLk353Me3Qi0A53iGmDF4hGSBJU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769081360; c=relaxed/simple; bh=WiogiOmlVrEBDmxiYq5jKojVlIXsrZ6n9wcQdU9VhMk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OPgrPlq5QZpjrv9139Z3RQV2z/BUJarWMgpUK2SCK9gy7iqxbVpFGEtWqYgMcsPeYB3v7GT+K2NsRR05dbX0pbK3h7IZh3oesYdazyiY/fDVNx3Ndy2RteVJCQKruEaBBR4Hxi/5VCc/VEjdFBCe6npYN8TzIFgQJ2Phs1/fo4s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hntVHlxv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hntVHlxv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CEAA5C116C6; Thu, 22 Jan 2026 11:29:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769081360; bh=WiogiOmlVrEBDmxiYq5jKojVlIXsrZ6n9wcQdU9VhMk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hntVHlxvRLtZcEpsFecgcuy2/WeJl9lYH2mWE9f8dZGjyucvG1zCLlgF1anVNM8Mq ATZwc6IftbgZO2kJLtftNKhMvBjvPvqfUNlH6JrZwPiiiEXtxPJi1HRA+GVlhwH0Xl 7jI4hCzwdhtpWuORobWzm0YF5J1jsS7gh1CwOGDB5EOeJZKzxHCuCd4SkLrzE/tlGq JVFBs8UA8NYTjNB18RHp1AShNa5zdE3qLITZrz7qt2dsO/+/eP32L9P7IpEILF4h3H 3+SL3O++ddzf33ljYPKdsDd6l1rT8hde2RP+XyHB6xkPeaAyuWp9p0Q+aK9fItrNc6 XJd/YpjN6/DQQ== Date: Thu, 22 Jan 2026 12:29:17 +0100 From: Frederic Weisbecker To: Will Deacon Cc: LKML , Michal =?iso-8859-1?Q?Koutn=FD?= , Andrew Morton , Bjorn Helgaas , Catalin Marinas , Chen Ridong , Danilo Krummrich , "David S . Miller" , Eric Dumazet , Gabriele Monaco , Greg Kroah-Hartman , Ingo Molnar , Jakub Kicinski , Jens Axboe , Johannes Weiner , Lai Jiangshan , Marco Crivellari , Michal Hocko , Muchun Song , Paolo Abeni , Peter Zijlstra , Phil Auld , "Rafael J . Wysocki" , Roman Gushchin , Shakeel Butt , Simon Horman , Tejun Heo , Thomas Gleixner , Vlastimil Babka , Waiman Long , cgroups@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH 29/33] sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN Message-ID: References: <20260101221359.22298-1-frederic@kernel.org> <20260101221359.22298-30-frederic@kernel.org> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Le Thu, Jan 22, 2026 at 09:56:29AM +0000, Will Deacon a écrit : > On Wed, Jan 21, 2026 at 06:06:07PM +0100, Frederic Weisbecker wrote: > > Le Tue, Jan 20, 2026 at 03:15:14PM +0000, Will Deacon a écrit : > > > Hi Frederic, > > > > > > On Thu, Jan 01, 2026 at 11:13:54PM +0100, Frederic Weisbecker wrote: > > > > When none of the allowed CPUs of a task are online, it gets migrated > > > > to the fallback cpumask which is all the non nohz_full CPUs. > > > > > > > > However just like nohz_full CPUs, domain isolated CPUs don't want to be > > > > disturbed by tasks that have lost their CPU affinities. > > > > > > > > And since nohz_full rely on domain isolation to work correctly, the > > > > housekeeping mask of domain isolated CPUs should always be a superset of > > > > the housekeeping mask of nohz_full CPUs (there can be CPUs that are > > > > domain isolated but not nohz_full, OTOH there shouldn't be nohz_full > > > > CPUs that are not domain isolated): > > > > > > > > HK_TYPE_DOMAIN | HK_TYPE_KERNEL_NOISE == HK_TYPE_DOMAIN > > > > > > > > Therefore use HK_TYPE_DOMAIN as the appropriate fallback target for > > > > tasks and since this cpumask can be modified at runtime, make sure > > > > that 32 bits support CPUs on ARM64 mismatched systems are not isolated > > > > by cpusets. > > > > > > > > Signed-off-by: Frederic Weisbecker > > > > Reviewed-by: Waiman Long > > > > --- > > > > arch/arm64/kernel/cpufeature.c | 18 +++++++++++++++--- > > > > include/linux/cpu.h | 4 ++++ > > > > kernel/cgroup/cpuset.c | 17 ++++++++++++++--- > > > > 3 files changed, 33 insertions(+), 6 deletions(-) > > > > > > tbh, I'd also be fine just saying that isolation isn't reliable on these > > > systems and then you don't need to add the extra arch hook. > > > > Hmm, I think I heard about nohz_full usage on arm64 but I'm not sure. > > And I usually expect isolcpus or cpuset isolated partitions to be even > > more broadly used, it's lighter isolation with less constraints. > > > > Anyway you're probably right that we could remove isolation support here > > but I don't want to break any existing user. > > fwiw, I think it's only some Android markets using the mismatched 32-bit > support and we're definitely not using nohz_full there. Now that removal becomes appealing. And what about isolcpus= / isolated cpuset which only consist in scheduler domain isolation? Probably not used by android either. Ok but is there a way to detect on early boot that the system has mismatched 32 bits support? Because I need to fail nohz_full= and isolcpus= boot parameters early on top of this information without waiting for secondary CPUs boot. Thanks. -- Frederic Weisbecker SUSE Labs