Re: Re: [PATCH] sched/fair: merge same code in enqueue_task_fair

[Abel Wu]

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@xxxxxxxxxxx> wrote:
> > > On Mon, Dec 11, 2023 at 04:23:52PM +0100, Vincent Guittot wrote:
> > > > On Sun, 10 Dec 2023 at 10:22, WangJinchao <wangjinchao@xxxxxxxxxxx> 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
> >