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

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Date:   Tue, 27 Jun 2023 16:08:07 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
CC:     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>,
        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 2023-06-26 at 10:09:10 -0700, Tim Chen wrote:
> 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?
>
I did not see noticeable extra throughput improvement from netperf, with
above change + Aaron's fix + Pan's cacheline alignment adjustment.

thanks,
Chenyu