linux-kernel - Re: [PATCH_V2] sched/fair: updates weight of cfs_rq before update_cfs_group() in enqueue

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Date: Tue, 11 Jun 2024 11:36:31 +0800
From: Gaowei Pu <pugaowei@...o.com>
To: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
 vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org,
 bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH_V2] sched/fair: updates weight of cfs_rq before
 update_cfs_group() in enqueue_entity()

ping...

On 2024/6/3 17:18, Gaowei.Pu wrote:
> From: pugaowei <pugaowei@...o.com>
> 
> we should update the weight of cfs_rq before update_cfs_group().
> Ensure that we can get accurate shares of the cfs_rq when its
> weights changes. we can find this work was done correctly in
> dequeue_entity(). so fix it.
> 
> patch_V1 :
> https://lore.kernel.org/lkml/20240531030833.3375-1-pugaowei@oppo.com/T/#u
> trigger a warnning below because of the changing order of
> account_entity_enqueue().
> 
> [ 0.400603][ T0] ? __warn (kernel/panic.c:693)
> 
> [ 0.400603][ T0] ? place_entity (kernel/sched/fair.c:5256 (discriminator 1))
> 
> [ 0.400603][ T0] ? report_bug (lib/bug.c:180 lib/bug.c:219)
> 
> [ 0.400603][ T0] ? handle_bug (arch/x86/kernel/traps.c:239)
> 
> [ 0.400603][ T0] ? exc_invalid_op (arch/x86/kernel/traps.c:260 (discriminator 1))
> 
> [ 0.400603][ T0] ? asm_exc_invalid_op (arch/x86/include/asm/idtentry.h:621)
> 
> [ 0.400603][ T0] ? place_entity (kernel/sched/fair.c:5256 (discriminator 1))
> 
> [ 0.400603][ T0] ? place_entity (kernel/sched/fair.c:5182)
> 
> [ 0.400603][ T0] enqueue_entity (kernel/sched/fair.c:5328)
> 
> [ 0.400603][ T0] enqueue_task_fair (kernel/sched/fair.c:6785)
> 
> V2 fix the warnning and keep the lag without inflating it when it is
> the first sched_entity queued on the cfs_rq.
> 
> Signed-off-by: pugaowei <pugaowei@...o.com>
> ---
>  kernel/sched/fair.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8a5b1ae0aa55..2fb1fbcfdda3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5190,12 +5190,12 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	 *
>  	 * EEVDF: placement strategy #1 / #2
>  	 */
> -	if (sched_feat(PLACE_LAG) && cfs_rq->nr_running) {
> +	if (sched_feat(PLACE_LAG)) {
>  		struct sched_entity *curr = cfs_rq->curr;
> -		unsigned long load;
> +		unsigned long load, se_load;
>  
>  		lag = se->vlag;
> -
> +		se_load = scale_load_down(se->load.weight);
>  		/*
>  		 * If we want to place a task and preserve lag, we have to
>  		 * consider the effect of the new entity on the weighted
> @@ -5252,9 +5252,13 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  		if (curr && curr->on_rq)
>  			load += scale_load_down(curr->load.weight);
>  
> -		lag *= load + scale_load_down(se->load.weight);
> -		if (WARN_ON_ONCE(!load))
> -			load = 1;
> +		lag *= load + se_load;
> +		/*
> +		 * we just need to keep the lag whithout inflating it when the se is
> +		 * the first sched_entity queued on cfs_rq.
> +		 */
> +		if (!load)
> +			load = se_load;
>  		lag = div_s64(lag, load);
>  	}
>  
> @@ -5304,6 +5308,12 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	 */
>  	update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH);
>  	se_update_runnable(se);
> +
> +	/*
> +	 * we should update the weight of cfs_rq before update_cfs_group.
> +	 * Ensure we can get accurate shares of the cfs_rq when its weights changes.
> +	 */
> +	account_entity_enqueue(cfs_rq, se);
>  	/*
>  	 * XXX update_load_avg() above will have attached us to the pelt sum;
>  	 * but update_cfs_group() here will re-adjust the weight and have to
> @@ -5318,8 +5328,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	if (!curr)
>  		place_entity(cfs_rq, se, flags);
>  
> -	account_entity_enqueue(cfs_rq, se);
> -
>  	/* Entity has migrated, no longer consider this task hot */
>  	if (flags & ENQUEUE_MIGRATED)
>  		se->exec_start = 0;