linux-kernel - Re: [PATCH v2] sched/task_group: Re-layout structure to reduce false sharing

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Message-ID: <0a611696cbc63a3a9b99a7966b8fe4f7e20a014b.camel@linux.intel.com>
Date:   Mon, 26 Jun 2023 10:09:10 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Chen Yu <yu.c.chen@...el.com>, Aaron Lu <aaron.lu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>
Cc:     Deng Pan <pan.deng@...el.com>, tim.c.chen@...el.com,
        linux-kernel@...r.kernel.org, tianyou.li@...el.com,
        yu.ma@...el.com, lipeng.zhu@...el.com
Subject: Re: [PATCH v2] sched/task_group: Re-layout structure to reduce
 false sharing

On Mon, 2023-06-26 at 15:52 +0800, Chen Yu wrote:
> 
>  
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index ec7b3e0a2b20..067f1310bad2 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1958,8 +1958,10 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
>  #endif
>  
>  #ifdef CONFIG_RT_GROUP_SCHED
> -	p->rt.rt_rq  = tg->rt_rq[cpu];
> -	p->rt.parent = tg->rt_se[cpu];
> +	if (p->sched_class = &rt_sched_class) {
> +		p->rt.rt_rq  = tg->rt_rq[cpu];
> +		p->rt.parent = tg->rt_se[cpu];
> +	}

If we avoid the assignment for non-rt task, do you see it further improves
c2c bounce?

Tim