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>
---
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