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Date: Thu, 2 Jun 2016 07:41:11 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Benjamin Segall <bsegall@google.com>, Paul Turner <pjt@google.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: [PATCH v3 2/5] sched/fair: Skip detach and attach new group task
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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".