linux-kernel - Re: [PATCH 1/2 v2] sched: fix find_idlest

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Date:   Mon, 28 Nov 2016 18:20:02 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Wanpeng Li <kernellwp@...il.com>,
        Yuyang Du <yuyang.du@...el.com>,
        Mike Galbraith <umgwanakikbuti@...il.com>
Subject: Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork

On 28 November 2016 at 18:01, Matt Fleming <matt@...eblueprint.co.uk> wrote:
> On Fri, 25 Nov, at 04:34:32PM, Vincent Guittot wrote:
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index aa47589..820a787 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5463,13 +5463,19 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
>>        * utilized systems if we require spare_capacity > task_util(p),
>>        * so we allow for some task stuffing by using
>>        * spare_capacity > task_util(p)/2.
>> +      * spare capacity can't be used for fork because the utilization has
>> +      * not been set yet as it need to get a rq to init the utilization
>>        */
>> +     if (sd_flag & SD_BALANCE_FORK)
>> +             goto no_spare;
>> +
>>       if (this_spare > task_util(p) / 2 &&
>>           imbalance*this_spare > 100*most_spare)
>>               return NULL;
>>       else if (most_spare > task_util(p) / 2)
>>               return most_spare_sg;
>>
>> +no_spare:
>>       if (!idlest || 100*this_load < imbalance*min_load)
>>               return NULL;
>>       return idlest;
>
> It's only a minor comment, but would you be opposed to calling this
> label 'skip_spare' to indicate that spare capacity may exist, but
> we're not going to make use of it?

you're right,  'skip_spare' makes more sense