Re: [PATCH v4 2/3] sched/fair: Clean up active balance nr_balance_failed trickery

[Dietmar Eggemann]

On 01/04/2021 21:30, Valentin Schneider wrote:
> When triggering an active load balance, sd->nr_balance_failed is set to
> such a value that any further can_migrate_task() using said sd will ignore
> the output of task_hot().
> 
> This behaviour makes sense, as active load balance intentionally preempts a
> rq's running task to migrate it right away, but this asynchronous write is
> a bit shoddy, as the stopper thread might run active_load_balance_cpu_stop
> before the sd->nr_balance_failed write either becomes visible to the
> stopper's CPU or even happens on the CPU that appended the stopper work.
> 
> Add a struct lb_env flag to denote active balancing, and use it in
> can_migrate_task(). Remove the sd->nr_balance_failed write that served the
> same purpose. Cleanup the LBF_DST_PINNED active balance special case.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

[...]