linux-kernel - Re: [PATCH 7/7 v2] sched/fair: Update overutilized detection

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Message-ID: <97c43712-f201-4565-92d1-f28af9da8ae8@arm.com>
Date: Fri, 17 Jan 2025 11:27:48 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, dietmar.eggemann@....com,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, lukasz.luba@....com, rafael.j.wysocki@...el.com,
 linux-kernel@...r.kernel.org
Cc: qyousef@...alina.io, hongyan.xia2@....com, christian.loehle@....com,
 qperret@...gle.com
Subject: Re: [PATCH 7/7 v2] sched/fair: Update overutilized detection

Hello Vincent,

On 12/17/24 17:07, Vincent Guittot wrote:
> Checking uclamp_min is useless and counterproductive for overutilized state
> as misfit can now happen without being in overutilized state

Before this patch a task was misfit if:
   !task_fits_cpu(p, cpu)
This is, if either:
- task_util > 80% * CPU_capacity
- task_UCLAMP_MIN > get_actual_cpu_capacity(cpu)

A CPU was OU if:
   !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu)
This is:
- CPU_util > 80% * CPU_capacity

This should be the same after this patch. Just to be sure I understand correctly,
this patch has no functional change and is independent from this serie right ?

> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>   kernel/sched/fair.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 9bddb094ee21..9eb4c4946ddc 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6870,16 +6870,15 @@ static inline void hrtick_update(struct rq *rq)
>   #ifdef CONFIG_SMP
>   static inline bool cpu_overutilized(int cpu)
>   {
> -	unsigned long  rq_util_min, rq_util_max;
> +	unsigned long rq_util_max;
>   
>   	if (!sched_energy_enabled())
>   		return false;
>   
> -	rq_util_min = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MIN);
>   	rq_util_max = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MAX);
>   
>   	/* Return true only if the utilization doesn't fit CPU's capacity */
> -	return !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu);
> +	return !util_fits_cpu(cpu_util_cfs(cpu), 0, rq_util_max, cpu);
>   }
>   
>   /*