[PATCH 1/1] sched/fair:Avoid unnecessary assignment to cfs_rq->on_list

[PATCH 1/1] sched/fair:Avoid unnecessary assignment to cfs_rq->on_list

[qianjun.kernel]

From: jun qian <qianjun.kernel@gmail.com>

Obviously, cfs_rq->on_list is already equal to 1 when cfs_rq->on_list
is assigned a value of 1, so an else branch is needed to avoid unnecessary
assignment operations.

Signed-off-by: jun qian <qianjun.kernel@gmail.com>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 04a3ce20da67..ef6ebd95443d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -305,8 +305,8 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 
 	if (cfs_rq->on_list)
 		return rq->tmp_alone_branch == &rq->leaf_cfs_rq_list;
-
-	cfs_rq->on_list = 1;
+	else
+		cfs_rq->on_list = 1;
 
 	/*
 	 * Ensure we either appear before our parent (if already
-- 
2.18.2

Re: [PATCH 1/1] sched/fair:Avoid unnecessary assignment to cfs_rq->on_list

[Vincent Guittot]

On Thu, 7 Jan 2021 at 02:57, <qianjun.kernel@gmail.com> wrote:
>
> From: jun qian <qianjun.kernel@gmail.com>
>
> Obviously, cfs_rq->on_list is already equal to 1 when cfs_rq->on_list
> is assigned a value of 1, so an else branch is needed to avoid unnecessary
> assignment operations.
>
> Signed-off-by: jun qian <qianjun.kernel@gmail.com>
> ---
>  kernel/sched/fair.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 04a3ce20da67..ef6ebd95443d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -305,8 +305,8 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
>
>         if (cfs_rq->on_list)
>                 return rq->tmp_alone_branch == &rq->leaf_cfs_rq_list;

if cfs_rq->on_list == 1, list_add_leaf_cfs_rq() returns and will not
unnecessary set cfs_rq->on_list

so your change is useless but makes the code less readable

> -
> -       cfs_rq->on_list = 1;
> +       else
> +               cfs_rq->on_list = 1;
>
>         /*
>          * Ensure we either appear before our parent (if already
> --
> 2.18.2
>