linux-kernel - Re: [PATCH 7/8] sched/fair: Do not compute overloaded status unnecessarily during lb

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Message-ID: <3ce396ad-162c-4e60-90ee-01fd58a514de@linux.ibm.com>
Date: Fri, 13 Dec 2024 20:27:43 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: "H. Peter Anvin" <hpa@...or.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Mario Limonciello <mario.limonciello@....com>,
        Meng Li <li.meng@....com>, Huang Rui <ray.huang@....com>,
        "Gautham R. Shenoy" <gautham.shenoy@....com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] sched/fair: Do not compute overloaded status
 unnecessarily during lb



On 12/12/24 00:25, K Prateek Nayak wrote:
> Only set sg_overloaded when computing sg_lb_stats() at the highest sched
> domain since rd->overloaded status is updated only when load balancing
> at the highest domain. While at it, move setting of sg_overloaded below
> idle_cpu() check since an idle CPU can never be overloaded.
> 
> Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
> ---
>   kernel/sched/fair.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ec2a79c8d0e7..3f36805ecdca 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10358,9 +10358,6 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>   		nr_running = rq->nr_running;
>   		sgs->sum_nr_running += nr_running;
>   
> -		if (nr_running > 1)
> -			*sg_overloaded = 1;
> -
>   		if (cpu_overutilized(i))
>   			*sg_overutilized = 1;

Maybe its worth moving the overutilized too after the idle checks. An 
idle cpu can't be overutilized right?

>   
> @@ -10373,6 +10370,10 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>   			continue;
>   		}
>   
> +		/* Overload indicator is only updated at root domain */
> +		if (!env->sd->parent && nr_running > 1)
> +			*sg_overloaded = 1;
> +
>   #ifdef CONFIG_NUMA_BALANCING
>   		/* Only fbq_classify_group() uses this to classify NUMA groups */
>   		if (sd_flags & SD_NUMA) {

Other than the point above,
Reviewed-by: Shrikanth Hegde <sshegde@...ux.ibm.com>