linux-kernel - Re: [PATCH v4 4/7] sched/fair: remove useless check in select_idle

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Message-ID: <73ab0143-b518-c0b5-328e-c8f3ec7013ed@bytedance.com>
Date:   Tue, 28 Jun 2022 11:51:01 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Josh Don <joshdon@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Chen Yu <yu.c.chen@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 4/7] sched/fair: remove useless check in
 select_idle_core


On 6/28/22 7:42 AM, Josh Don Wrote:
> On Sun, Jun 19, 2022 at 5:05 AM Abel Wu <wuyun.abel@...edance.com> wrote:
>>
>> The function only gets called when sds->has_idle_cores is true which can
>> be possible only when sched_smt_present is enabled.
>>
>> Signed-off-by: Abel Wu <wuyun.abel@...edance.com>
>> ---
>>   kernel/sched/fair.c | 3 ---
>>   1 file changed, 3 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index aba1dad19574..1cc86e76e38e 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6256,9 +6256,6 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
>>          bool idle = true;
>>          int cpu;
>>
>> -       if (!static_branch_likely(&sched_smt_present))
>> -               return __select_idle_cpu(core, p);
>> -
> 
> The static branch is basically free; although you're right that we
> currently don't take !smt_present branch direction here, it doesn't
> seem harmful to leave this check in case assumptions change about when
> we call select_idle_core().

I was thinking that it would be better to align with select_idle_smt
that the caller do the check if necessary.

> 
>>          for_each_cpu(cpu, cpu_smt_mask(core)) {
>>                  if (!available_idle_cpu(cpu)) {
>>                          idle = false;
>> --
>> 2.31.1
>>