Re: [PATCH] sched: update the rq->avg_idle when a task is moved to an idle CPU

[Shijie Huang <shijie@amperemail.onmicrosoft.com>]

On 25/11/2025 15:08, Madadi Vineeth Reddy wrote:
> I traced the activate_task() call paths and found that load balancing migrations
> through attach_task() in kernel/sched/fair.c may not be covered.
thanks for pointing this, I did not notice them.
>
> activate_task <- attach_task <- attach_tasks <- sched_balance_rq
> activate_task <- attach_task <- attach_one_task <- active_load_balance_cpu_stop
>
> These paths are called in periodic load balancing and when tasks are pulled
> towards an idle CPU via attach_task(), it doesn't update rq->avg_idle or clear
> idle_stamp.

Yes, we should update the rq->avg_idle for them.

I will add it in version 2.

>
> Should attach_task() in kernel/sched/fair.c also call update_rq_avg_idle()
> after activation?

IMHO,  we should not call the update_rq_avg_idle() directly in 
attach_task().

In the current attach_task(), there is no information for the 
context(newidle, idle, busy).

The attach_task() is also called in the newidle code path.

But we can call the update_rq_avg_idle() in attach_tasks() with a 
condition check.

>
> Also, can update_rq_avg_idle() be placed inside activate_task() to avoid
> all these?

The same reason as above.


Thanks

Huang Shijie