linux-kernel - Re: [PATCH] sched/fair: Fix cfs_rq_is

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Message-ID: <0e29059a-7f1c-523d-c3ec-e17bbc094af9@linux.dev>
Date:   Fri, 18 Aug 2023 21:17:32 +0800
From:   Chengming Zhou <chengming.zhou@...ux.dev>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, ycliang@...estech.com,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        zhouchengming@...edance.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Fix cfs_rq_is_decayed() on !SMP

On 2023/8/18 20:25, Vincent Guittot wrote:
> On Fri, 18 Aug 2023 at 13:37, <chengming.zhou@...ux.dev> wrote:
>>
>> From: Chengming Zhou <zhouchengming@...edance.com>
>>
>> We don't need to maintain per-queue leaf_cfs_rq_list on !SMP, since
>> it's used for cfs_rq load tracking & balance on SMP.
>>
>> But sched debug interface use it to print per-cfs_rq stats, which
>> maybe better to change to use walk_tg_tree_from() instead.
>>
>> This patch just fix the !SMP version cfs_rq_is_decayed(), so the
>> per-queue leaf_cfs_rq_list is also maintained correctly on !SMP,
>> to fix the warning in assert_list_leaf_cfs_rq().
>>
>> Fixes: 0a00a354644e ("sched/fair: Delete useless condition in tg_unthrottle_up()")
>> Reported-by: Leo Liang <ycliang@...estech.com>
>> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
>> ---
>>  kernel/sched/fair.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index a80a73909dc2..00ef7e86a95b 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -4654,6 +4654,8 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
>>
>>  static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
>>  {
>> +       if (cfs_rq->load.weight)
>> +               return false;
>>         return true;
> 
> Why not :
> 
> return !(cfs_rq->nr_running);
> 
> The above seems easier to understand although I agree that both do the
> same thing at the end
> 

Yes, this is better.

Thanks.