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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 , Will Deacon , 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: [PATCH 29/33] sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN Date: Sun, 25 Jan 2026 23:45:36 +0100 Message-ID: <20260125224541.50226-30-frederic@kernel.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20260125224541.50226-1-frederic@kernel.org> References: <20260125224541.50226-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 97B5B1C0005 X-Rspamd-Server: rspam07 X-Stat-Signature: z6sd7gb1oqreqap1siwsruk9dgxifcbm X-HE-Tag: 1769381389-212208 X-HE-Meta: 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 IuKvRzrc JxI4lPNVzvZ7cbMisCJqpTb4A1GBFygaaRQsoQm7MOcrTY0mzDxoY1yLOoiMVsiodjZGLEOLJzldfKcD8GSZvGBuOZCO97txXTAbKfX1z6gHixRFMjRlaesRL/76xrK5nTTnYcnYLknXcoB6JiHFuiExjg/Gb6Lv1SrR0PF6ivZAQ8i6J5XCUwS2aUkiQvDSHu+niZAlZQhngcntgNR2GexU4eT/X3b8U8ircV+puRvSwV6AHPU3PEwJOh6Z6gJRYGrq+C+VFm9rW/W0W24xWANp5WF2jtHejcf4eCgUdF/N/hyAh4T0K2GJ76A== 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: 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 subset 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. Note that cpuset isolated partitions are not supported on those systems and may result in undefined behaviour. Signed-off-by: Frederic Weisbecker Reviewed-by: Waiman Long --- Documentation/arch/arm64/asymmetric-32bit.rst | 12 ++++++++---- arch/arm64/kernel/cpufeature.c | 6 +++--- 2 files changed, 11 insertions(+), 7 deletions(-) diff --git a/Documentation/arch/arm64/asymmetric-32bit.rst b/Documentation/arch/arm64/asymmetric-32bit.rst index 57b8d7476f71..fc0c350c5e00 100644 --- a/Documentation/arch/arm64/asymmetric-32bit.rst +++ b/Documentation/arch/arm64/asymmetric-32bit.rst @@ -154,10 +154,14 @@ mode will return to host userspace with an ``exit_reason`` of ``KVM_EXIT_FAIL_ENTRY`` and will remain non-runnable until successfully re-initialised by a subsequent ``KVM_ARM_VCPU_INIT`` operation. -NOHZ FULL ---------- +SCHEDULER DOMAIN ISOLATION +-------------------------- -To avoid perturbing an adaptive-ticks CPU (specified using -``nohz_full=``) when a 32-bit task is forcefully migrated, these CPUs +To avoid perturbing a boot-defined domain isolated CPU (specified using +``isolcpus=[domain]``) when a 32-bit task is forcefully migrated, these CPUs are treated as 64-bit-only when support for asymmetric 32-bit systems is enabled. + +However as opposed to boot-defined domain isolation, runtime-defined domain +isolation using cpuset isolated partition is not advised on asymmetric +32-bit systems and will result in undefined behaviour. diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index c840a93b9ef9..f0e66cb27d17 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1669,7 +1669,7 @@ const struct cpumask *system_32bit_el0_cpumask(void) const struct cpumask *task_cpu_fallback_mask(struct task_struct *p) { - return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_TICK)); + return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_DOMAIN)); } static int __init parse_32bit_el0_param(char *str) @@ -3987,8 +3987,8 @@ static int enable_mismatched_32bit_el0(unsigned int cpu) bool cpu_32bit = false; if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) { - if (!housekeeping_cpu(cpu, HK_TYPE_TICK)) - pr_info("Treating adaptive-ticks CPU %u as 64-bit only\n", cpu); + if (!housekeeping_cpu(cpu, HK_TYPE_DOMAIN)) + pr_info("Treating domain isolated CPU %u as 64-bit only\n", cpu); else cpu_32bit = true; } -- 2.51.1