[PATCH 00/33 v3] cpuset/isolation: Honour kthreads preferred affinity

Frederic Weisbecker
2025-10-13T20:32:02Z

Hi,

The kthread code was enhanced lately to provide an infrastructure which
manages the preferred affinity of unbound kthreads (node or custom
cpumask) against housekeeping constraints and CPU hotplug events.

One crucial missing piece is cpuset: when an isolated partition is
created, deleted, or its CPUs updated, all the unbound kthreads in the
top cpuset are affine to _all_ the non-isolated CPUs, possibly breaking
their preferred affinity along the way

Solve this with performing the kthreads affinity update from cpuset to
the kthreads consolidated relevant code instead so that preferred
affinities are honoured.

The dispatch of the new cpumasks to workqueues and kthreads is performed
by housekeeping, as per the nice Tejun's suggestion.

As a welcome side effect, HK_TYPE_DOMAIN then integrates both the set
from isolcpus= and cpuset isolated partitions. Housekeeping cpumasks are
now modifyable with specific synchronization. A big step toward making
nohz_full= also mutable through cpuset in the future.

Changes since v2:

* Keep static key (peterz)

* Handle PCI work flush

* Comment why RCU is held until PCI work is queued (Waiman)

* Add new tags

* Add CONFIG_LOCKDEP ifdeffery (Waiman)

* Rename workqueue_unbound_exclude_cpumask() to workqueue_unbound_housekeeping_update()
and invert the parameter (Waiman)

* Fix a few changelogs that used to mention that HK_TYPE_KERNEL_NOISE
must depend on HK_TYPE_DOMAIN. It's strongly advised but not mandatory (Waiman)

* Cherry-pick latest version of "cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping"
(Waiman and Gabriele)

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
kthread/core-v3

HEAD: 4ba707cdced479592e9f461e1944b7fa6f75910f

Thanks,
Frederic
---

Frederic Weisbecker (32):
PCI: Prepare to protect against concurrent isolated cpuset change
cpu: Revert "cpu/hotplug: Prevent self deadlock on CPU hot-unplug"
memcg: Prepare to protect against concurrent isolated cpuset change
mm: vmstat: Prepare to protect against concurrent isolated cpuset change
sched/isolation: Save boot defined domain flags
cpuset: Convert boot_hk_cpus to use HK_TYPE_DOMAIN_BOOT
driver core: cpu: Convert /sys/devices/system/cpu/isolated to use HK_TYPE_DOMAIN_BOOT
net: Keep ignoring isolated cpuset change
block: Protect against concurrent isolated cpuset change
cpu: Provide lockdep check for CPU hotplug lock write-held
cpuset: Provide lockdep check for cpuset lock held
sched/isolation: Convert housekeeping cpumasks to rcu pointers
cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset
sched/isolation: Flush memcg workqueues on cpuset isolated partition change
sched/isolation: Flush vmstat workqueues on cpuset isolated partition change
PCI: Flush PCI probe workqueue on cpuset isolated partition change
cpuset: Propagate cpuset isolation update to workqueue through housekeeping
cpuset: Remove cpuset_cpu_is_isolated()
sched/isolation: Remove HK_TYPE_TICK test from cpu_is_isolated()
PCI: Remove superfluous HK_TYPE_WQ check
kthread: Refine naming of affinity related fields
kthread: Include unbound kthreads in the managed affinity list
kthread: Include kthreadd to the managed affinity list
kthread: Rely on HK_TYPE_DOMAIN for preferred affinity management
sched: Switch the fallback task allowed cpumask to HK_TYPE_DOMAIN
sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN
kthread: Honour kthreads preferred affinity after cpuset changes
kthread: Comment on the purpose and placement of kthread_affine_node() call
kthread: Add API to update preferred affinity on kthread runtime
kthread: Document kthread_affine_preferred()
genirq: Correctly handle preferred kthreads affinity
doc: Add housekeeping documentation

Gabriele Monaco (1):
cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping

Documentation/cpu_isolation/housekeeping.rst | 111 +++++++++++++++
arch/arm64/kernel/cpufeature.c | 18 ++-
block/blk-mq.c | 6 +-
drivers/base/cpu.c | 2 +-
drivers/pci/pci-driver.c | 71 +++++++---
include/linux/cpu.h | 4 +
include/linux/cpuhplock.h | 1 +
include/linux/cpuset.h | 8 +-
include/linux/kthread.h | 2 +
include/linux/memcontrol.h | 4 +
include/linux/mmu_context.h | 2 +-
include/linux/pci.h | 3 +
include/linux/percpu-rwsem.h | 1 +
include/linux/sched/isolation.h | 7 +-
include/linux/vmstat.h | 2 +
include/linux/workqueue.h | 2 +-
init/Kconfig | 1 +
kernel/cgroup/cpuset.c | 134 +++++++++++++-----
kernel/cpu.c | 42 +++---
kernel/irq/manage.c | 47 ++++---
kernel/kthread.c | 195 +++++++++++++++++++--------
kernel/sched/isolation.c | 137 +++++++++++++++----
kernel/sched/sched.h | 4 +
kernel/workqueue.c | 17 ++-
mm/memcontrol.c | 25 +++-
mm/vmstat.c | 15 ++-
net/core/net-sysfs.c | 2 +-
27 files changed, 647 insertions(+), 216 deletions(-)