The Linux kernel provides mechanisms like 'isolcpus' and 'nohz_full' to reduce interference for latency-sensitive workloads. However, these are locked behind the "Reboot Wall" - they can only be configured via boot parameters and require a system restart to change.
*** THIS IS AN RFC *** This series is being submitted as an Request For Comments to discuss the architectural changes required to support dynamic reconfiguration of housekeeping boundaries. Key points for discussion: - The use of a blocking notifier chain for cross-subsystem synchronization. - Compatibility with existing boot-time isolcpus and nohz_full parameters. - User-space sysfs interface design for granular isolation control. While cgroup2 (cpuset) provides task-centric resource partitioning (including unbound kthreads), it lacks the infrastructure to reconfigure core kernel subsystems or manage per-CPU kernel activities. Specifically, cgroups cannot: - Managed interrupt (IRQ) migration. - RCU callback offloading and grace-period kthread placement. - Per-CPU kernel threads (e.g., watchdog/n) and global subsystem logic (e.g., kcompactd). - Subsystem-level masks for unbound workqueues. - Dynamic toggling of full dynticks (NOHZ_FULL) mode. This patch series introduces Dynamic Housekeeping & Enhanced Isolation (DHEI). DHEI allows administrators to reconfigure the kernel's housekeeping boundaries at runtime via a new sysfs interface at /sys/kernel/housekeeping/. Core Architecture: 1. Notifier-Driven Synchronization: A new blocking notifier chain (HK_UPDATE_MASK) allows isolation.c to signal all participating subsystems (IRQ, RCU, Sched, Watchdog, Workqueue, kcompactd, Tick) whenever a housekeeping mask is modified. 2. Decoupled Memory Management: Replaced boot-time memory allocators with runtime-safe variants, allowing masks to be allocated or resized after the system is running. 3. Subsystem Handlers: Each critical subsystem implements a reconfiguration handler to migrate pending work, re-affine kthreads, or re-route interrupts dynamically. Key Features: - Fine-grained control: Separate sysfs nodes for timer, rcu, tick, workqueue, kthread, etc. - Dynamic NOHZ_FULL: Supports enabling/disabling full dynticks mode on-the-fly by re-kicking CPUs to evaluate tick dependencies. - SMT Awareness: An optional 'smt_aware_mode' ensures that all SMT siblings of a physical core stay in the same isolation state. - Safety Guard: Prevents the isolation of all CPUs, ensuring at least one online CPU is always available for housekeeping tasks. This series provides the necessary infrastructure for cloud-native orchestrators and high-frequency trading platforms to dynamically re-partition CPU resources without incurring the downtime of a reboot. Signed-off-by: Qiliang Yuan <[email protected]> --- Qiliang Yuan (12): sched/isolation: Remove __init restriction from housekeeping cores sched/isolation: Introduce reconfiguration notifier chain genirq: Implement dynamic migration for Managed IRQs rcu: Sync RCU housekeeping mask on notification sched/core: Dynamic update housekeeping_cpumask(HK_TYPE_DOMAIN) watchdog: Allow runtime toggle of hardlockup detector on CPUs workqueue: Dynamic housekeeping mask update support kcompactd: Add housekeeping notifier for dynamic mask update sched/isolation: Separate housekeeping types and add sysfs interface tick/nohz: Implement dynamic nohz_full state update sched/isolation: Implement SMT sibling auto-isolation and safety check sched/isolation: Bridge isolcpus and support runtime tick offload init include/linux/sched/isolation.h | 40 +++++-- include/linux/tick.h | 2 +- kernel/irq/manage.c | 52 +++++++++ kernel/rcu/tree.c | 43 +++++++ kernel/sched/core.c | 5 +- kernel/sched/isolation.c | 252 ++++++++++++++++++++++++++++++++++++++-- kernel/sched/sched.h | 2 +- kernel/sched/topology.c | 26 +++++ kernel/time/tick-sched.c | 63 +++++++++- kernel/watchdog.c | 24 ++++ kernel/workqueue.c | 39 +++++++ mm/compaction.c | 26 +++++ 12 files changed, 547 insertions(+), 27 deletions(-) --- base-commit: 1f97d9dcf53649c41c33227b345a36902cbb08ad change-id: 20260206-feature-dynamic_isolcpus_dhei-ee46b6e3a477 Best regards, -- Qiliang Yuan <[email protected]>
