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 A717A1531E8; Tue, 20 Jan 2026 15:15:24 +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=1768922124; cv=none; b=V3U0MhiT5NKSuT7OLQICbIXOtNe5C/oKaTyCsIqTPx3LwMa/OpvLuTO7GMLazPAUhN+OtjlE1B2XwLosM0SH5qRVXcJ3OXi8jhzud9EZ2H7tir26p7QXuLbfWsm6pF/c7orGsmXctScJtN7kUbX6vWLItDfzUs1cfNyyeGuYTuw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768922124; c=relaxed/simple; bh=cB6+u0cGFM+BuA6s4Sw76CjAr/+izfs5ypcZfWumP+8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=EzEy85kqJ/2Z+LMoThi5rMTg30Nv+y4s5oJbfL6KtV1t6+EM9nk+x7tOnQemBr2j1V/QCxZoozQV6tdQ+dx/ojGdxFbb0bcPAVFqCnNoYpPPtS6uVaBCHUjcDguU83O7RU/XIImmqztEh8xsCBsXySbCmjruTmCoWjT5gi21C40= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dTm6pm0U; 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="dTm6pm0U" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B042EC16AAE; Tue, 20 Jan 2026 15:15:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768922124; bh=cB6+u0cGFM+BuA6s4Sw76CjAr/+izfs5ypcZfWumP+8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dTm6pm0UbqrACPX84K25WsKI0mLcsga30LnGZ0xAs1QeHOq8GuYQb0tsVAj/1PyOk AN1JtPlGK2Lo1SN6drBYr1dVy9fdgzrRQCr2v1Zr5WaI0DgPDkYpbpHSPBc0lzPVxT mDodJS2/jqZjTXVaKaFD5qjNt2270SzYmLSpr9NA2qekfz0PdVSlZLmHpnEvNYJ+eY A07k9S1Ry7xxwMicubb01dCJM4tNlasnq386AOzVL87vqKI0T34pSKz9QNypV2LDxE 2HWPcTW6E/V+Ce+TphpVMpakDh1WcI3tzKUwZtHRXG5Gb8k9H87NfGW6D+dQQz/FfZ kpuAsAsDnxf/g== Date: Tue, 20 Jan 2026 15:15:14 +0000 From: Will Deacon To: Frederic Weisbecker 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: 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: <20260101221359.22298-30-frederic@kernel.org> 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. Whatever you prefer, but please can you update the text in Documentation/arch/arm64/asymmetric-32bit.rst to cover the interaction between the asymmetric stuff and cpu isolation? Cheers, Will