linux-kernel - Re: [PATCH 13/15] sched,fair: propagate sum_exec

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Message-ID: <f940abf6-3020-014c-74d7-d9be334e201c@arm.com>
Date:   Wed, 28 Aug 2019 09:51:36 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org
Cc:     kernel-team@...com, pjt@...gle.com, peterz@...radead.org,
        mingo@...hat.com, morten.rasmussen@....com, tglx@...utronix.de,
        mgorman@...hsingularity.net, vincent.guittot@...aro.org
Subject: Re: [PATCH 13/15] sched,fair: propagate sum_exec_runtime up the
 hierarchy

On 22/08/2019 04:17, Rik van Riel wrote:
> Now that enqueue_task_fair and dequeue_task_fair no longer iterate up
> the hierarchy all the time, a method to lazily propagate sum_exec_runtime
> up the hierarchy is necessary.
> 
> Once a tick, propagate the newly accumulated exec_runtime up the hierarchy,
> and feed it into CFS bandwidth control.
> 
> Remove the pointless call to account_cfs_rq_runtime from update_curr,
> which is always called with a root cfs_rq.

But what about the call to account_cfs_rq_runtime() in
set_curr_task_fair()? Here you always call it with the root cfs_rq.
Shouldn't this be called also in a loop over all se's until !se->parent
(like in propagate_exec_runtime() further below).

> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  include/linux/sched.h |  1 +
>  kernel/sched/core.c   |  1 +
>  kernel/sched/fair.c   | 22 ++++++++++++++++++++--
>  3 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 901c710363e7..bdca15b3afe7 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -454,6 +454,7 @@ struct sched_entity {
>  	int				depth;
>  	unsigned long			enqueued_h_load;
>  	unsigned long			enqueued_h_weight;
> +	u64				propagated_exec_runtime;
>  	struct load_weight		h_load;
>  	struct sched_entity		*parent;
>  	/* rq on which this entity is (to be) queued: */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index fbd96900f715..9915d20e84a9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2137,6 +2137,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>  	INIT_LIST_HEAD(&p->se.group_node);
>  
>  #ifdef CONFIG_FAIR_GROUP_SCHED
> +	p->se.propagated_exec_runtime	= 0;
>  	p->se.cfs_rq			= NULL;
>  #endif
>  
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5cfa3dbeba49..d6c881c5c4d5 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -898,8 +898,6 @@ static void update_curr(struct cfs_rq *cfs_rq)
>  	trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
>  	cgroup_account_cputime(curtask, delta_exec);
>  	account_group_exec_runtime(curtask, delta_exec);
> -
> -	account_cfs_rq_runtime(cfs_rq, delta_exec);
>  }
>  
>  static void update_curr_fair(struct rq *rq)
> @@ -3412,6 +3410,20 @@ static inline bool skip_blocked_update(struct sched_entity *se)
>  	return true;
>  }
>  
> +static void propagate_exec_runtime(struct cfs_rq *cfs_rq,
> +				struct sched_entity *se)
> +{
> +	struct sched_entity *parent = se->parent;
> +	u64 diff = se->sum_exec_runtime - se->propagated_exec_runtime;
> +
> +	if (parent) {
> +		parent->sum_exec_runtime += diff;
> +		account_cfs_rq_runtime(cfs_rq, diff);
> +	}
> +
> +	se->propagated_exec_runtime = se->sum_exec_runtime;
> +}
> +
>  #else /* CONFIG_FAIR_GROUP_SCHED */
>  
>  static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force) {}
> @@ -3423,6 +3435,11 @@ static inline int propagate_entity_load_avg(struct sched_entity *se)
>  
>  static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum) {}
>  
> +static void propagate_exec_runtime(struct cfs_rq *cfs_rq,
> +				struct sched_entity *se);
> +{
> +}
> +
>  #endif /* CONFIG_FAIR_GROUP_SCHED */
>  
>  /**
> @@ -10157,6 +10174,7 @@ static void propagate_entity_cfs_rq(struct sched_entity *se, int flags)
>  			if (!(flags & DO_ATTACH))
>  				break;
>  
> +		propagate_exec_runtime(cfs_rq, se);
>  		update_cfs_group(se);
>  	}
>  }
>