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Date:   Wed, 16 Dec 2020 09:44:32 +0000
From:   xiaoggchen(陈小光) <xiaoggchen@...cent.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "chenxg1x@...il.com" <chenxg1x@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "bsegall@...gle.com" <bsegall@...gle.com>,
        "mgorman@...e.de" <mgorman@...e.de>,
        "bristot@...hat.com" <bristot@...hat.com>,
        heddchen(陈贺) <heddchen@...cent.com>
Subject: 答复: [PATCH] sched: don't check rq after newidle_balance return positive(Internet mail)



-----邮件原件-----
发件人: Peter Zijlstra <peterz@...radead.org> 
发送时间: 2020年12月15日 16:33
收件人: chenxg1x@...il.com
抄送: linux-kernel@...r.kernel.org; mingo@...hat.com; juri.lelli@...hat.com; vincent.guittot@...aro.org; dietmar.eggemann@....com; rostedt@...dmis.org; bsegall@...gle.com; mgorman@...e.de; bristot@...hat.com; heddchen(陈贺) <heddchen@...cent.com>; xiaoggchen(陈小光) <xiaoggchen@...cent.com>
主题: Re: [PATCH] sched: don't check rq after newidle_balance return positive(Internet mail)

On Tue, Dec 15, 2020 at 02:48:50PM +0800, chenxg1x@...il.com wrote:
>> From: Chen Xiaoguang <xiaoggchen@...cent.com>
>> 
>> In pick_next_task_fair, if CPU is going to idle newidle_balance is 
>> called first trying to pull some tasks.
>> When newidle_balance returns positive which means it does pulls tasks 
>> or some tasks enqueued then there is no need to check 
>> sched_fair_runnable again.

> No, I think it actually does need to, because while it counts the number of tasks it pulled, it doesn't verify it still has them after it re-acquires rq->lock. That is, someone could've come along and stolen them 
> right from under our noses.
Ah, yes, our change only make sense when pulling nothing in load_balance but some tasks enqueued this rq during the lock of this rq is released.
 
Thanks.

>> 
>> Signed-off-by: He Chen <heddchen@...cent.com>
>> Signed-off-by: Xiaoguang Chen <xiaoggchen@...cent.com>

> This SoB chain is broken. The first SoB should be the author, but From does not match.
We will fix this next time.

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