Re: [PATCH 3/3] sched: Use cpu_dying() to fix balance_push vs hotplug-rollback

[Valentin Schneider <valentin.schneider@arm.com>]

On 15/04/21 10:59, Peter Zijlstra wrote:
> Can't make sense of what I did.. I've removed that hunk. Patch now looks
> like this.
>

Small nit below, but regardless feel free to apply to the whole lot:
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

@VincentD, ISTR you had tested the initial version of this with your fancy
shmancy hotplug rollback stresser. Feel like doing this

> So instead, make sure balance_push is enabled between
> sched_cpu_deactivate() and sched_cpu_activate() (eg. when
> !cpu_active()), and gate it's utility with cpu_dying().

I'd word that "is enabled below sched_cpu_activate()", since
sched_cpu_deactivate() is now out of the picture.

[...]
> @@ -7639,6 +7639,9 @@ static DEFINE_PER_CPU(struct cpu_stop_wo
>
>  /*
>   * Ensure we only run per-cpu kthreads once the CPU goes !active.
> + *
> + * This is active/set between sched_cpu_deactivate() / sched_cpu_activate().

Ditto

> + * But only effective when the hotplug motion is down.
>   */
>  static void balance_push(struct rq *rq)
>  {