linux-kernel - Re: [PATCH 09/14] sched,fair: refactor enqueue/dequeue

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Date:   Tue, 30 Jul 2019 11:36:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rik van Riel <riel@...riel.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        dietmar.eggemann@....com, mingo@...hat.com,
        morten.rasmussen@....com, tglx@...utronix.de,
        mgorman@...hsingularity.net, vincent.guittot@...aro.org
Subject: Re: [PATCH 09/14] sched,fair: refactor enqueue/dequeue_entity

On Mon, Jul 22, 2019 at 01:33:43PM -0400, Rik van Riel wrote:
> Refactor enqueue_entity, dequeue_entity, and update_load_avg, in order
> to split out the things we still want to happen at every level in the
> cgroup hierarchy with a flat runqueue from the things we only need to
> happen once.
> 
> No functional changes.

> @@ -3500,7 +3500,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
>  #define DO_ATTACH	0x4
>  
>  /* Update task and its cfs_rq load average */
> -static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> +static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  {
>  	u64 now = cfs_rq_clock_pelt(cfs_rq);
>  	int decayed;
> @@ -3529,6 +3529,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
>  
>  	} else if (decayed && (flags & UPDATE_TG))
>  		update_tg_load_avg(cfs_rq, 0);
> +
> +	return decayed;
>  }
>  
>  #ifndef CONFIG_64BIT
> @@ -3745,9 +3747,10 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
>  #define SKIP_AGE_LOAD	0x0
>  #define DO_ATTACH	0x0
>  
> -static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
> +static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
>  {
>  	cfs_rq_util_change(cfs_rq, 0);
> +	return false;
>  }
>  
>  static inline void remove_entity_load_avg(struct sched_entity *se) {}
> @@ -3870,6 +3873,24 @@ static inline void check_schedstat_required(void)
>   * CPU and an up-to-date min_vruntime on the destination CPU.
>   */
>  
> +static bool
> +enqueue_entity_groups(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> +{
> +	/*
> +	 * When enqueuing a sched_entity, we must:
> +	 *   - Update loads to have both entity and cfs_rq synced with now.
> +	 *   - Add its load to cfs_rq->runnable_avg
> +	 *   - For group_entity, update its weight to reflect the new share of
> +	 *     its group cfs_rq
> +	 *   - Add its new weight to cfs_rq->load.weight
> +	 */
> +	if (!update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH))
> +		return false;
> +
> +	update_cfs_group(se);
> +	return true;
> +}
> +
>  static void
>  enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  {
> @@ -3894,16 +3915,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	if (renorm && !curr)
>  		se->vruntime += cfs_rq->min_vruntime;
>  
> -	/*
> -	 * When enqueuing a sched_entity, we must:
> -	 *   - Update loads to have both entity and cfs_rq synced with now.
> -	 *   - Add its load to cfs_rq->runnable_avg
> -	 *   - For group_entity, update its weight to reflect the new share of
> -	 *     its group cfs_rq
> -	 *   - Add its new weight to cfs_rq->load.weight
> -	 */
> -	update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH);
> -	update_cfs_group(se);
>  	enqueue_runnable_load_avg(cfs_rq, se);
>  	account_entity_enqueue(cfs_rq, se);
>  

No functional, but you did make update_cfs_group() conditional. Now that
looks OK, but maybe you can do that part in a separate patch with a
little justification of its own.