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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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: 8udd8mx6we1974odesdmcxsxi9ikhsx7 X-Rspamd-Queue-Id: 6C5611A000B X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1769081361-674346 X-HE-Meta: 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 O522ms1q cXUVPaP8cag4XcFvfR0S2HG1f+FtCoJDERFhBjYe0CR6Ar5a3/P9UfJy5PRNh31/LnlupJnlEkvYQvru/hR/yB2HHS8C2t+CL1JwuNrL85HvQDuU8fMK2AvfiDScE8/bydysrT3HriM+LEW/3MRus/ZEwbCRDD7Sz6Y/y+sD5U50G4AeBUM8lM6aP/9/rthaBnZz1i2vlUBQJodi4elUkUtRGNuizWDF4dcH8Zd6pTuASPicQGwpCMVpu/U9cb2VVnxWolwrUxiiJ5kDavb0NG9ggFSHQ0oQ/WkRmIrVe1s8Qid1Kk13OBdSO3m+7+Ig0D/ioSJ3kTvUJxQU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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