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SubjectRe: [PATCH v7 6/7] sched: replace capacity_factor by usage
On 9 October 2014 16:16, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Oct 07, 2014 at 02:13:36PM +0200, Vincent Guittot wrote:
>> @@ -6214,17 +6178,21 @@ 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 to one 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. group_capacity > 0. 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 &&
>> + group_has_capacity(env, &sds->local_stat)) {
>> + if (sgs->sum_nr_running > 1)
>> + sgs->group_no_capacity = 1;
>> + sgs->group_capacity = min(sgs->group_capacity,
>> + SCHED_CAPACITY_SCALE);
>> + }
>>
>> if (update_sd_pick_busiest(env, sds, sg, sgs)) {
>> sds->busiest = sg;
>
>> @@ -6490,8 +6460,8 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
>> goto force_balance;
>>
>> /* SD_BALANCE_NEWIDLE trumps SMP nice when underutilized */
>> - if (env->idle == CPU_NEWLY_IDLE && local->group_has_free_capacity &&
>> - !busiest->group_has_free_capacity)
>> + if (env->idle == CPU_NEWLY_IDLE && group_has_capacity(env, local) &&
>> + busiest->group_no_capacity)
>> goto force_balance;
>>
>> /*
>
> This is two calls to group_has_capacity() on the local group. Why not
> compute once in update_sd_lb_stats()?

mainly because of the place in the code, so it is not always used
during load balance unlike group_no_capacity

Now that i have said that, i just noticed that it's better to move the
call to the last tested condition

+ if (env->idle == CPU_NEWLY_IDLE && busiest->group_no_capacity &&
+ group_has_capacity(env, local))


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