linux-kernel - Re: [PATCH 2/4] sched/eevdf: Update se->vprot in reweight

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Message-ID: <CAKfTPtDFB0Eg652fUh8M-jj3y=u=ie1zqAoRmCPUu+r6pz-qhQ@mail.gmail.com>
Date: Fri, 30 Jan 2026 17:20:57 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, juri.lelli@...hat.com, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, 
	linux-kernel@...r.kernel.org, wangtao554@...wei.com, quzicheng@...wei.com, 
	kprateek.nayak@....com, wuyun.abel@...edance.com, dsmythies@...us.net, 
	Zhang Qiao <zhangqiao22@...wei.com>
Subject: Re: [PATCH 2/4] sched/eevdf: Update se->vprot in reweight_entity()

On Fri, 30 Jan 2026 at 10:47, Peter Zijlstra <peterz@...radead.org> wrote:
>
> From: Wang Tao <wangtao554@...wei.com>
>
> In the EEVDF framework with Run-to-Parity protection, `se->vprot` is an
> independent variable defining the virtual protection timestamp.
>
> When `reweight_entity()` is called (e.g., via nice/renice), it performs
> the following actions to preserve Lag consistency:
>  1. Scales `se->vlag` based on the new weight.
>  2. Calls `place_entity()`, which recalculates `se->vruntime` based on
>     the new weight and scaled lag.
>
> However, the current implementation fails to update `se->vprot`, leading
> to mismatches between the task's actual runtime and its expected duration.
>
> Fixes: 63304558ba5d ("sched/eevdf: Curb wakeup-preemption")
> Suggested-by: Zhang Qiao <zhangqiao22@...wei.com>
> Signed-off-by: Wang Tao <wangtao554@...wei.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

> Link: https://patch.msgid.link/20260120123113.3518950-1-wangtao554@huawei.com
> ---
>  kernel/sched/fair.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3790,6 +3790,8 @@ static void reweight_entity(struct cfs_r
>                             unsigned long weight)
>  {
>         bool curr = cfs_rq->curr == se;
> +       bool rel_vprot = false;
> +       u64 vprot;
>
>         if (se->on_rq) {
>                 /* commit outstanding execution time */
> @@ -3797,6 +3799,11 @@ static void reweight_entity(struct cfs_r
>                 update_entity_lag(cfs_rq, se);
>                 se->deadline -= se->vruntime;
>                 se->rel_deadline = 1;
> +               if (curr && protect_slice(se)) {
> +                       vprot = se->vprot - se->vruntime;
> +                       rel_vprot = true;
> +               }
> +
>                 cfs_rq->nr_queued--;
>                 if (!curr)
>                         __dequeue_entity(cfs_rq, se);
> @@ -3812,6 +3819,9 @@ static void reweight_entity(struct cfs_r
>         if (se->rel_deadline)
>                 se->deadline = div_s64(se->deadline * se->load.weight, weight);
>
> +       if (rel_vprot)
> +               vprot = div_s64(vprot * se->load.weight, weight);
> +
>         update_load_set(&se->load, weight);
>
>         do {
> @@ -3823,6 +3833,8 @@ static void reweight_entity(struct cfs_r
>         enqueue_load_avg(cfs_rq, se);
>         if (se->on_rq) {
>                 place_entity(cfs_rq, se, 0);
> +               if (rel_vprot)
> +                       se->vprot = se->vruntime + vprot;
>                 update_load_add(&cfs_rq->load, se->load.weight);
>                 if (!curr)
>                         __enqueue_entity(cfs_rq, se);
>
>