From 79c0abaf06fca6e715cf792daed580542fc4a2c4 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 24 Jul 2025 23:38:48 +0200 Subject: [PATCH] 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 Reviewed-by: Waiman Long Acked-by: Will Deacon Tested-by: Will Deacon Cc: Catalin Marinas Cc: Marco Crivellari Cc: Michal Hocko Cc: Peter Zijlstra Cc: Tejun Heo Cc: Thomas Gleixner Cc: Waiman Long Cc: Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org --- 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 57b8d7476f71b..fc0c350c5e001 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 c840a93b9ef95..f0e66cb27d179 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; } -- 2.47.3