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

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Message-ID: <CAKfTPtBPkBu0qbOm3fPhbDZAa6t=aW6VE9bps_9k8dmA0k3=cw@mail.gmail.com>
Date:	Thu, 2 Jun 2016 09:40:18 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Yuyang Du <yuyang.du@...el.com>
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 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