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

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Date:   Thu, 14 Dec 2023 17:47:57 +0800
From:   Wang Jinchao <wangjinchao@...sion.com>
To:     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: [PATCH] sched/fair: merge same code in enqueue_task_fair

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%

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
>