On Thu, Oct 15, 2026 at 12:00:25PM -0400, Waiman Long wrote: > On 10/15/26 8:43 AM, Peng Wang wrote: > > Workloads and their need for periodic ticks can change after boot. > > This series lets userspace choose at runtime which CPUs in the boot-time > > nohz_full set retain the non-idle scheduler tick and which are permitted > > to stop it, while preserving the existing isolation configuration. > > > > The first patch adds a per-CPU tick dependency; the second exposes a > > sysfs CPU list. Permission defaults to all nohz_full CPUs. Revocation > > uses the existing asynchronous kick. Idle tick suppression is unchanged, > > and policy persists across hotplug. > So you are basically setting up more nohz_full CPUs than the system actually > needs to use at the moment and so want to disable nohz/tick part of > nohz_full CPUs that don't need it. Can you elaborate more about the problems > solve by introducing this new behavior?
Hi Waiman, Yes. We have CPU-pinned workloads that benefit from reduced periodic tick interference. The desired tick policy changes with CPU allocation. With spare capacity, we allow selected nohz_full CPUs to stop their tick. When capacity is fully allocated, we prefer to retain the non-idle periodic tick across CPUs, avoiding an additional difference in tick interference between housekeeping and nohz_full CPUs. A CPU may still have only one runnable task in either case, so the existing tick dependencies do not express this policy. This series keeps the boot-time nohz_full CPU set, context tracking, RCU offloading and housekeeping configuration unchanged. It only controls whether those CPUs may stop their non-idle tick. The policy can be changed without taking CPUs offline. > > > > Existing cpuset partition modes do not express this independent tick > > policy. Feedback on the proposed interface is welcome. > > We are planning to eventually extend cpuset partition mode to change > nohz_full at runtime. This is still a work in progress. Thanks for mentioning the cpuset work. Would this tick-only policy fit into that plan? The core mechanism in patch 1 is independent of the sysfs interface. Thanks, Peng > > Regards, > Longman > > > > > Thanks, > > Peng > > > > Peng Wang (2): > > tick/nohz: Add a policy dependency for full dynticks > > cpu: Add sysfs control of full dynticks policy > > > > .../ABI/testing/sysfs-devices-system-cpu | 40 ++++++++++++ > > drivers/base/cpu.c | 46 ++++++++++++++ > > include/linux/tick.h | 8 ++- > > include/trace/events/timer.h | 3 +- > > kernel/time/tick-sched.c | 62 +++++++++++++++++++ > > 5 files changed, 156 insertions(+), 3 deletions(-) > > > > > > base-commit: 0fcb05b72344f40806cbe810de8872f1698bf053 >
