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

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Date:   Thu, 14 Dec 2023 20:42:23 +0800
From:   Wang Jinchao <wangjinchao@...sion.com>
To:     Abel Wu <wuyun.abel@...edance.com>
CC:     Vincent Guittot <vincent.guittot@...aro.org>,
        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 Thu, Dec 14, 2023 at 08:10:57PM +0800, Abel Wu wrote:
> 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.
Agree. My initinal target is clear comprehension.
And thanks for your numbers.
> 
> > 
> > 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
> > >