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From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Fri, 27 Mar 2015 16:59:52 +0100
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Subject: Re: [PATCH v10 08/11] sched: replace capacity_factor by usage
To: Xunlei Pang <pang.xunlei@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        Rik van Riel <riel@redhat.com>,
        Linaro Kernel Mailman List <linaro-kernel@lists.linaro.org>,
        Mike Galbraith <efault@gmx.de>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>
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On 27 March 2015 at 15:52, Xunlei Pang <pang.xunlei@linaro.org> wrote:
> Hi Vincent,
>
> On 27 February 2015 at 23:54, Vincent Guittot
> <vincent.guittot@linaro.org> wrote:
>>  /**
>> @@ -6432,18 +6435,19 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>>
>>                 /*
>>                  * In case the child domain prefers tasks go to siblings
>> -                * first, lower the sg capacity factor to one so that we'll try
>> +                * first, lower the sg capacity so that we'll try
>>                  * and move all the excess tasks away. We lower the capacity
>>                  * of a group only if the local group has the capacity to fit
>> -                * these excess tasks, i.e. nr_running < group_capacity_factor. The
>> -                * extra check prevents the case where you always pull from the
>> -                * heaviest group when it is already under-utilized (possible
>> -                * with a large weight task outweighs the tasks on the system).
>> +                * these excess tasks. The extra check prevents the case where
>> +                * you always pull from the heaviest group when it is already
>> +                * under-utilized (possible with a large weight task outweighs
>> +                * the tasks on the system).
>>                  */
>>                 if (prefer_sibling && sds->local &&
>> -                   sds->local_stat.group_has_free_capacity) {
>> -                       sgs->group_capacity_factor = min(sgs->group_capacity_factor, 1U);
>> -                       sgs->group_type = group_classify(sg, sgs);
>> +                   group_has_capacity(env, &sds->local_stat) &&
>> +                   (sgs->sum_nr_running > 1)) {
>> +                       sgs->group_no_capacity = 1;
>> +                       sgs->group_type = group_overloaded;
>>                 }
>>
>
> For SD_PREFER_SIBLING, if local has 1 task and group_has_capacity()
> returns true(but not overloaded)  for it, and assume sgs group has 2
> tasks, should we still mark this group overloaded?

yes, the load balance will then choose if it's worth pulling it or not
depending of the load of each groups

>
> -Xunlei