linux-kernel - Re: [PATCH 4/4] sched/fair: Improve NO_RUN_TO

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Message-ID: <3xnsz5DduwrP5NZ4fLZuWCqqljSUXjsZ4rP9oiX-ojKy8iQiLE6ukWqn0V6f_iC_jNsKNzdwSSCqkthvPLjB9_uLumSLU8AbeH0BbpptxzY=@gianis.ca>
Date: Fri, 13 Jun 2025 22:55:11 +0000
From: dhaval@...nis.ca
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: mingo@...hat.com, peterz@...radead.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
Subject: Re: [PATCH 4/4] sched/fair: Improve NO_RUN_TO_PARITY






On Friday, June 13th, 2025 at 7:15 AM, Vincent Guittot <vincent.guittot@...aro.org> wrote:

> 
> 
> The slice protection of RUN_TO_PARITY should also be applied with a
> minimal quantum of time for NO_RUN_TO_PARITY in order to ensure a minimum
> runtime for each task with same slice duration but also to ensure
> periodic switch between threads.
> 
> Signed-off-by: Vincent Guittot vincent.guittot@...aro.org
> 
> ---
> kernel/sched/fair.c | 22 ++++++++++++----------
> 1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d8345219dfd4..73bde511c53b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -921,15 +921,20 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
> * one in vlag, which isn't used until dequeue.
> * In case of run to parity, we use the shortest slice of the enqueued
> * entities.
> + * When run to parity is disable we give a minimum quantum to the

"disabled"

> + * running entity to ensure progress.
> */
> static inline void set_protect_slice(struct sched_entity *se)
> {
> - u64 min_slice;
> + u64 quantum;
> 
> - min_slice = cfs_rq_min_slice(cfs_rq_of(se));
> + if (sched_feat(RUN_TO_PARITY))
> + quantum = cfs_rq_min_slice(cfs_rq_of(se));
> + else
> + quantum = min(se->slice, normalized_sysctl_sched_base_slice);
> 
> 
> - if (min_slice != se->slice)
> 
> - se->vlag = min(se->deadline, se->vruntime + calc_delta_fair(min_slice, se));
> 
> + if (quantum != se->slice)
> 
> + se->vlag = min(se->deadline, se->vruntime + calc_delta_fair(quantum, se));
> 
> else
> se->vlag = se->deadline;
> 
> }
> @@ -981,7 +986,7 @@ static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq)
> if (curr && (!curr->on_rq || !entity_eligible(cfs_rq, curr)))
> 
> curr = NULL;
> 
> - if (sched_feat(RUN_TO_PARITY) && curr && protect_slice(curr))
> + if (curr && protect_slice(curr))
> return curr;
> 
> /* Pick the leftmost entity if it's eligible */
> @@ -1215,11 +1220,8 @@ static inline void update_curr_task(struct task_struct *p, s64 delta_exec)
> cgroup_account_cputime(p, delta_exec);
> }
> 
> -static inline bool did_preempt_short(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> +static inline bool resched_next_quantum(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> {
> - if (!sched_feat(PREEMPT_SHORT))
> - return false;
> -
> if (protect_slice(curr))
> return false;
> 
> @@ -1307,7 +1309,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
> if (cfs_rq->nr_queued == 1)
> 
> return;
> 
> - if (resched || did_preempt_short(cfs_rq, curr)) {
> + if (resched || resched_next_quantum(cfs_rq, curr)) {
> resched_curr_lazy(rq);
> clear_buddies(cfs_rq, curr);
> }
> --
> 2.43.0