Re: [tip: sched/hrtick] sched/eevdf: Fix HRTICK duration

[Shrikanth Hegde]

Sorry for very very late reply. I was trying to go through this.

On 2/28/26 9:07 PM, tip-bot2 for Peter Zijlstra wrote:
> The following commit has been merged into the sched/hrtick branch of tip:
>
> Commit-ID:     558c18d3fbb6c5b9c0b42629d7fe34476363ac00
> Gitweb:        https://git.kernel.org/tip/558c18d3fbb6c5b9c0b42629d7fe34476363ac00
> Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> AuthorDate:    Tue, 24 Feb 2026 17:35:17 +01:00
> Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> CommitterDate: Fri, 27 Feb 2026 16:40:03 +01:00
>
> sched/eevdf: Fix HRTICK duration
>
> The nominal duration for an EEVDF task to run is until its deadline. At
> which point the deadline is moved ahead and a new task selection is done.
>
> Try and predict the time 'lost' to higher scheduling classes. Since this is
> an estimate, the timer can be both early or late. In case it is early
> task_tick_fair() will take the !need_resched() path and restarts the timer.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Reviewed-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
> Link: https://patch.msgid.link/20260224163428.798198874@xxxxxxxxxx
> ---
>   kernel/sched/fair.c | 41 +++++++++++++++++++++++++++--------------
>   1 file changed, 27 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index eea99ec..247fecd 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6735,21 +6735,37 @@ static inline void sched_fair_update_stop_tick(struct rq *rq, struct task_struct
>   static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
>   {
>   	struct sched_entity *se = &p->se;
> +	unsigned long scale = 1024;
> +	unsigned long util = 0;
> +	u64 vdelta;
> +	u64 delta;
>   
>   	WARN_ON_ONCE(task_rq(p) != rq);
>   
> -	if (rq->cfs.h_nr_queued > 1) {
> -		u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
> -		u64 slice = se->slice;
> -		s64 delta = slice - ran;
> +	if (rq->cfs.h_nr_queued <= 1)
> +		return;
>   
> -		if (delta < 0) {
> -			if (task_current_donor(rq, p))
> -				resched_curr(rq);
> -			return;
> -		}
> -		hrtick_start(rq, delta);
> +	/*
> +	 * Compute time until virtual deadline
> +	 */
> +	vdelta = se->deadline - se->vruntime;
> +	if ((s64)vdelta < 0) {
> +		if (task_current_donor(rq, p))
> +			resched_curr(rq);
> +		return;
>   	}
> +	delta = (se->load.weight * vdelta) / NICE_0_LOAD;
> +
> +	/*
> +	 * Correct for instantaneous load of other classes.
> +	 */
> +	util += cpu_util_irq(rq);
> +	if (util && util < 1024) {
> +		scale *= 1024;
> +		scale /= (1024 - util);
> +	}

Comments/Changelog says other classes.

Then why not consider cpu_util_dl, cpu_util_rq too?
Is there a reason why these are not taken into calculations?

> +
> +	hrtick_start(rq, (scale * delta) / 1024);
>   }
>   
>   /*
> @@ -13365,11 +13381,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
>   		entity_tick(cfs_rq, se, queued);
>   	}
>   
> -	if (queued) {
> -		if (!need_resched())
> -			hrtick_start_fair(rq, curr);
> +	if (queued)
>   		return;
> -	}
>   
>   	if (static_branch_unlikely(&sched_numa_balancing))
>   		task_tick_numa(rq, curr);