linux-kernel - Re: [PATCH] sched/fair: Simplify the code of should_we

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Date:   Mon, 13 Apr 2020 21:32:37 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peng Wang <rocking@...ux.alibaba.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Simplify the code of should_we_balance()


On 12/04/20 09:42, Peng Wang wrote:
> On 4/11/20 5:20 PM, Peng Wang wrote:
>> We only consider group_balance_cpu() after there is no idle
>> cpu. So, just do comparison before return at these two cases.
>>

It's not really changing much, but if it helps making it a bit more
readable, why not. Small nit below.

Reviewed-by: Valentin Schneider <valentin.schneider@....com>

>> Signed-off-by: Peng Wang <rocking@...ux.alibaba.com>
>> ---
>>   kernel/sched/fair.c | 16 +++++-----------
>>   1 file changed, 5 insertions(+), 11 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 1ea3ddd..81b2c647 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -9413,7 +9413,7 @@ static int active_load_balance_cpu_stop(void *data);
>>   static int should_we_balance(struct lb_env *env)
>>   {
>>      struct sched_group *sg = env->sd->groups;
>> -	int cpu, balance_cpu = -1;
>> +	int cpu;
>>
>>      /*
>>       * Ensure the balancing environment is consistent; can happen
>> @@ -9434,18 +9434,12 @@ static int should_we_balance(struct lb_env *env)
>>              if (!idle_cpu(cpu))
>>                      continue;
>>
>> -		balance_cpu = cpu;
>> -		break;
>> +		/* Are we the first idle CPU? */
>> +		return cpu == env->dst_cpu;
>>      }
>>
>> -	if (balance_cpu == -1)
>> -		balance_cpu = group_balance_cpu(sg);
>> -
>> -	/*
>> -	 * First idle CPU or the first CPU(busiest) in this sched group
>> -	 * is eligible for doing load balancing at this and above domains.
>> -	 */
>> -	return balance_cpu == env->dst_cpu;
>> +	/* Are we the first balance CPU of this group? */

Nit: That should be either "the balance CPU" or "the first CPU in the group
balance mask"

>> +	return group_balance_cpu(sg) == env->dst_cpu;
>>   }
>>
>>   /*
>>
>
> +juri.lelli@...hat.com