Re: [PATCH 03/23] tick/nohz: Make nohz_full parameter optional

Thomas Gleixner
2026-04-21T08:32:24Z

On Mon, Apr 20 2026 at 23:03, Waiman Long wrote:
> To provide nohz_full tick support, there is a set of tick dependency
> masks that need to be evaluated on every IRQ and context switch.

s/IRQ/interrupt/

This is a changelog and not a SMS service.

> Switching on nohz_full tick support at runtime will be problematic
> as some of the tick dependency masks may not be properly set causing
> problem down the road.

That's useless blurb with zero content.

> Allow nohz_full boot option to be specified without any
> parameter to force enable nohz_full tick support without any
> CPU in the tick_nohz_full_mask yet. The context_tracking_key and
> tick_nohz_full_running flag will be enabled in this case to make
> tick_nohz_full_enabled() return true.

I kinda can crystal-ball what you are trying to say here, but that does
not make it qualified as a proper change log.

> There is still a small performance overhead by force enable nohz_full
> this way. So it should only be used if there is a chance that some
> CPUs may become isolated later via the cpuset isolated partition
> functionality and better CPU isolation closed to nohz_full is desired.

Why has this key to be enabled on boot if there are no CPUs in the
isolated mask?

If you want to manage this dynamically at runtime then enable the key
once CPUs are isolated. Yes, it's more work, but that avoids the "should
only be used" nonsense and makes this more robust down the road.

Thanks,

tglx