Re: [PATCH] Sched/fair: Block nohz tick_stop when cfs bandwidth in use

[Steven Rostedt]

On Thu, 22 Jun 2023 09:27:51 -0400
Phil Auld <pauld@xxxxxxxxxx> wrote:

> CFS bandwidth limits and NOHZ full don't play well together.  Tasks
> can easily run well past their quotas before a remote tick does
> accounting.  This leads to long, multi-period stalls before such
> tasks can run again. Currentlyi, when presented with these conflicting
> requirements the scheduler is favoring nohz_full and letting the tick
> be stopped. However, nohz tick stopping is already best-effort, there
> are a number of conditions that can prevent it, whereas cfs runtime
> bandwidth is expected to be enforced.
> 
> Make the scheduler favor bandwidth over stopping the tick by setting
> TICK_DEP_BIT_SCHED when the only running task is a cfs task with
> runtime limit enabled.
> 
> Add sched_feat HZ_BW (off by default) to control this behavior.

So the tl;dr; is: "If the current task has a bandwidth limit, do not disable
the tick" ?

-- Steve