Re: [PATCH v6 2/2] sched: update the rq->avg_idle when a task is moved to an idle CPU

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 12.12.25 04:16, Shijie Huang wrote:
> 
> On 12/12/2025 00:15, Dietmar Eggemann wrote:
>> In v2 you moved update_rq_avg_idle() (1) from activate_task() (2) to
>> enqueue_task() to possibly handle delayed tasks.
> Not for the delayed tasks, just for a more common place to handle more
> cases.
>> In v3 you figured there can't be any delayed task on a CPU when it sets
>> rq->idle_stamp in sched_balance_newidle()
> Yes.
>> So you could move (1) back to (2) avoiding the 'if rq->idle_stamp' for
>> the sched_change pattern for instance?
> Could you please tell me what is "avoiding the 'if rq->idle_stamp' for
> the sched_change pattern" ?
> 
> Sorry, I do not understand your meaning.

sched_change uses dequeue_task()/enqueue_task() for a queued task to
change prio, policy, sched params, taskgroups, etc.

kernel/sched/sched.h:

DEFINE_CLASS(sched_change, struct sched_change_ctx *,
             sched_change_end(_T),
             sched_change_begin(p, flags),
             struct task_struct *p, unsigned int flags)

kernel/sched/core.c:

struct sched_change_ctx *sched_change_begin(struct task_struct *p,
unsigned int flags)

void sched_change_end(struct sched_change_ctx *ctx)

> IMHO, there is no need to move (1) back to (2).

Btw, I'm using a BUG_ON(this_rq->idle_stamp) in sched_balance_newidle()
with update_rq_avg_idle() in activate_task() for testing.