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sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN

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 <frederic@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Acked-by: Will Deacon <will@kernel.org>
Tested-by: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org

Frederic Weisbecker 79c0abaf bf5b0c27

+11 -7
+8 -4
Documentation/arch/arm64/asymmetric-32bit.rst
··· 154 154 ``KVM_EXIT_FAIL_ENTRY`` and will remain non-runnable until successfully 155 155 re-initialised by a subsequent ``KVM_ARM_VCPU_INIT`` operation. 156 156 157 - NOHZ FULL 158 - --------- 157 + SCHEDULER DOMAIN ISOLATION 158 + -------------------------- 159 159 160 - To avoid perturbing an adaptive-ticks CPU (specified using 161 - ``nohz_full=``) when a 32-bit task is forcefully migrated, these CPUs 160 + To avoid perturbing a boot-defined domain isolated CPU (specified using 161 + ``isolcpus=[domain]``) when a 32-bit task is forcefully migrated, these CPUs 162 162 are treated as 64-bit-only when support for asymmetric 32-bit systems 163 163 is enabled. 164 + 165 + However as opposed to boot-defined domain isolation, runtime-defined domain 166 + isolation using cpuset isolated partition is not advised on asymmetric 167 + 32-bit systems and will result in undefined behaviour.
+3 -3
arch/arm64/kernel/cpufeature.c
··· 1669 1669 1670 1670 const struct cpumask *task_cpu_fallback_mask(struct task_struct *p) 1671 1671 { 1672 - return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_TICK)); 1672 + return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_DOMAIN)); 1673 1673 } 1674 1674 1675 1675 static int __init parse_32bit_el0_param(char *str) ··· 3987 3987 bool cpu_32bit = false; 3988 3988 3989 3989 if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) { 3990 - if (!housekeeping_cpu(cpu, HK_TYPE_TICK)) 3991 - pr_info("Treating adaptive-ticks CPU %u as 64-bit only\n", cpu); 3990 + if (!housekeeping_cpu(cpu, HK_TYPE_DOMAIN)) 3991 + pr_info("Treating domain isolated CPU %u as 64-bit only\n", cpu); 3992 3992 else 3993 3993 cpu_32bit = true; 3994 3994 }