linux-kernel - Re: [PATCH v5 2/2] sched/fair: update scale invariance of PELT

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Date:   Wed, 31 Oct 2018 08:20:44 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, peterz@...radead.org,
        mingo@...nel.org, linux-kernel@...r.kernel.org
Cc:     rjw@...ysocki.net, Morten.Rasmussen@....com,
        patrick.bellasi@....com, pjt@...gle.com, bsegall@...gle.com,
        thara.gopinath@...aro.org, pkondeti@...eaurora.org
Subject: Re: [PATCH v5 2/2] sched/fair: update scale invariance of PELT

On 10/26/18 6:11 PM, Vincent Guittot wrote:

[...]

>   static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
>   static unsigned long task_h_load(struct task_struct *p);
> @@ -764,7 +763,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
>   			 * such that the next switched_to_fair() has the
>   			 * expected state.
>   			 */
> -			se->avg.last_update_time = cfs_rq_clock_task(cfs_rq);
> +			se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
>   			return;
>   		}
>   	}

There is this 1/cpu scaling of se->avg.util_sum (running_sum) in 
update_tg_cfs_runnable() so it can be used to calculate 
se->avg.runnable_load_sum (runnable_sum). I guess with your approach 
this should be removed.

> @@ -3466,7 +3465,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
>   /* 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)
>   {
> -	u64 now = cfs_rq_clock_task(cfs_rq);
> +	u64 now = cfs_rq_clock_pelt(cfs_rq);
>   	struct rq *rq = rq_of(cfs_rq);
>   	int cpu = cpu_of(rq);
>   	int decayed;
> @@ -6694,6 +6693,12 @@ done: __maybe_unused;
>   	if (new_tasks > 0)
>   		goto again;
>   
> +	/*
> +	 * rq is about to be idle, check if we need to update the
> +	 * lost_idle_time of clock_pelt
> +	 */
> +	update_idle_rq_clock_pelt(rq);
> +
>   	return NULL;
>   }

[...]