linux-kernel - Re: [PATCH v3 2/5] sched/fair: Skip detach and attach new group task

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Date:	Thu, 2 Jun 2016 07:50:58 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v3 2/5] sched/fair: Skip detach and attach new group task

On Thu, Jun 02, 2016 at 09:40:18AM +0200, Vincent Guittot wrote:
> On 2 June 2016 at 01:41, Yuyang Du <yuyang.du@...el.com> wrote:
> > On Thu, Jun 02, 2016 at 09:29:53AM +0200, Vincent Guittot wrote:
> >> > My response to your above two comments:
> >> >
> >> > As I said, there can be four possibilities going through the above sequences:
> >> >
> >> > (1) on_rq, (2) !on_rq, (a) was fair class (representing last_update_time != 0),
> >> > (b) never was fair class (representing last_update_time == 0, but may not be
> >> > limited to this)
> >> >
> >> > Crossing them, we have (1)(a), (1)(b), (2)(a), and (2)(b).
> >> >
> >> > Some will attach twice, which are (1)(b) and (2)(b), the other will attach
> >> > once, which are (1)(a) and (2)(a). The difficult part is they can be attached
> >> > at different places.
> >>
> >> ok for (1)(b) but not for (2)(b) and it's far from "attached mostly
> >> twice every time"
> >
> > You are right. That claim is reckless, I will change it to:
> > "sometimes attached twice".
> 
> Or you can just describe the used case (1)(b) which is the only one AFAICT

You are right again, ;)