linux-kernel - Re: Re: [PATCH] sched/fair: merge same code in enqueue_task

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Date:   Thu, 14 Dec 2023 20:10:57 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Wang Jinchao <wangjinchao@...sion.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, stone.xulei@...sion.com
Subject: Re: Re: [PATCH] sched/fair: merge same code in enqueue_task_fair

On 12/14/23 5:47 PM, Wang Jinchao Wrote:
> On Wed, Dec 13, 2023 at 09:23:46AM +0100, Vincent Guittot wrote:
>> On Wed, 13 Dec 2023 at 08:04, Wang Jinchao <wangjinchao@...sion.com> wrote:
>>>
>>> On Mon, Dec 11, 2023 at 04:23:52PM +0100, Vincent Guittot wrote:
>>>> On Sun, 10 Dec 2023 at 10:22, WangJinchao <wangjinchao@...sion.com> wrote:
>>>>>
>>>>> 1. The code below is duplicated in two for loops and need to be
>>>>>     consolidated
>>>>> 2. Fix the bug where a se's on_rq is true but its parent is not
>>>>
>>>> Could you clarify which bug you want to fix ?
>>> Taking into account the additional information provided by Tim,
>>> this is not a bug. Therefore, this patch is merely a logical
>>> simplification.
>>
>> If there is no bug why changing it ?
> For two reasons:
> 1. (from Abel Wu)
> It doesn't need to, but it can actually bring some benefit from
> the point of view of text size, especially in warehouse-scale
> computers where icache is extremely contended.
> 
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-56 (-56)
> Function                                     old     new   delta
> enqueue_task_fair                            936     880     -56
> Total: Before=64899, After=64843, chg -0.09%

But TBH this benefit is kind of weak to argue about, given that you
don't have any data supporting it.

> 
> 2. For better code comprehension
> I became curious when I reached this part, wondering why there is a lot of
> repetition inside these two for-loops. Then I thought about 'do not repeat yourself,'
> and I feel that merging them would lead to a clearer understanding. Of course,
> it might be because I am just starting to read scheduler-related code and am not
> yet familiar with the entire logic.
>>
>> The duplication is done in order to have the same pattern in :
>> enqueue_task_fair
>> dequeue_task_fair
>> throttle_cfs_rq
>> unthrottle_cfs_rq
> Due to the two points mentioned above, do we need to adjust all four functions?
>>
>> so there is no need to change it
> I plan to get familiar with the scheduler-related code first and then consider this.
> 
> Thanks
>>