答复: [PATCH] sched: don't check rq after newidle_balance return positive(Internet mail)

["xiaoggchen(陈小光)" <xiaoggchen@tencent.com>]

-----邮件原件-----
发件人: Peter Zijlstra <peterz@infradead.org> 
发送时间: 2020年12月15日 16:33
收件人: chenxg1x@gmail.com
抄送: linux-kernel@vger.kernel.org; mingo@redhat.com; juri.lelli@redhat.com; vincent.guittot@linaro.org; dietmar.eggemann@arm.com; rostedt@goodmis.org; bsegall@google.com; mgorman@suse.de; bristot@redhat.com; heddchen(陈贺) <heddchen@tencent.com>; xiaoggchen(陈小光) <xiaoggchen@tencent.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@gmail.com wrote:
>> From: Chen Xiaoguang <xiaoggchen@tencent.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@tencent.com>
>> Signed-off-by: Xiaoguang Chen <xiaoggchen@tencent.com>

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