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

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Message-ID: <DM6PR11MB3260FC52E13ADB32AB745DFC9627A@DM6PR11MB3260.namprd11.prod.outlook.com>
Date:   Tue, 27 Jun 2023 14:52:50 +0000
From:   "Deng, Pan" <pan.deng@...el.com>
To:     "Chen, Yu C" <yu.c.chen@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>
CC:     "Lu, Aaron" <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>,
        "Chen, Tim C" <tim.c.chen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Li, Tianyou" <tianyou.li@...el.com>, "Ma, Yu" <yu.ma@...el.com>,
        "Zhu, Lipeng" <lipeng.zhu@...el.com>
Subject: RE: [PATCH v2] sched/task_group: Re-layout structure to reduce false
 sharing



> -----Original Message-----
> From: Chen, Yu C <yu.c.chen@...el.com>
> Sent: Tuesday, June 27, 2023 4:08 PM
> To: Tim Chen <tim.c.chen@...ux.intel.com>
> Cc: Lu, Aaron <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>; Chen, Tim C <tim.c.chen@...el.com>; linux-
> kernel@...r.kernel.org; Li, Tianyou <tianyou.li@...el.com>; Ma, Yu
> <yu.ma@...el.com>; Zhu, Lipeng <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.

Echo Yu.
Cacheline alignment adjustment resolved set_task_rq c2c bounce with load_avg,
The remained cycles of "assignment for non-rt task" is little according to perf record
data, the should be the reason of no extra throughput improvement.

Thanks
Pan 
> 
> thanks,
> Chenyu