linux-kernel - Re: [PATCH v3 2/7] sched: make struct sched_statistics independent of fair sched class

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Date:   Tue, 31 Aug 2021 12:19:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     mingo@...hat.com, mgorman@...e.de, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, bristot@...hat.com,
        achaiken@...ora.tech, lkp@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH v3 2/7] sched: make struct sched_statistics independent
 of fair sched class

On Tue, Aug 24, 2021 at 11:29:41AM +0000, Yafang Shao wrote:

> +#ifdef CONFIG_FAIR_GROUP_SCHED
> +static inline void
> +__schedstats_from_sched_entity(struct sched_entity *se,
> +			      struct sched_statistics **stats)
> +{
> +	struct task_group *tg;
> +	struct task_struct *p;
> +	struct cfs_rq *cfs;
> +	int cpu;
> +
> +	if (entity_is_task(se)) {
> +		p = task_of(se);
> +		*stats = &p->stats;
> +	} else {
> +		cfs = group_cfs_rq(se);
> +		tg = cfs->tg;
> +		cpu = cpu_of(rq_of(cfs));
> +		*stats = tg->stats[cpu];
> +	}
> +}
> +
> +#else
> +
> +static inline void
> +__schedstats_from_sched_entity(struct sched_entity *se,
> +			      struct sched_statistics **stats)
> +{
> +	struct task_struct *p;
> +
> +	p = task_of(se);
> +	*stats = &p->stats;
> +}
> +
> +#endif
> +
>  /*
>   * Update the current task's runtime statistics.
>   */
> @@ -826,6 +861,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
>  {
>  	struct sched_entity *curr = cfs_rq->curr;
>  	u64 now = rq_clock_task(rq_of(cfs_rq));
> +	struct sched_statistics *stats = NULL;
>  	u64 delta_exec;
>  
>  	if (unlikely(!curr))
> @@ -837,8 +873,11 @@ static void update_curr(struct cfs_rq *cfs_rq)
>  
>  	curr->exec_start = now;
>  
> -	schedstat_set(curr->statistics.exec_max,
> -		      max(delta_exec, curr->statistics.exec_max));
> +	if (schedstat_enabled()) {
> +		__schedstats_from_sched_entity(curr, &stats);
> +		__schedstat_set(stats->exec_max,
> +				max(delta_exec, stats->exec_max));
> +	}
>  
>  	curr->sum_exec_runtime += delta_exec;
>  	schedstat_add(cfs_rq->exec_clock, delta_exec);


That's just really odd style; what's wrong with something like:

static inline struct sched_statistics *
__schedstats_from_se(struct sched_entity *se)
{
	...
}

	if (schedstats_enabled()) {
		struct sched_statistics *stats = __schedstats_from_se(curr);
		__schedstat_set(stats->exec_max, max(stats->exec_max, delta_exec));
	}