Hi Vincent,
On 27 March 2015 at 23:59, Vincent Guittot <vincent.guit...@linaro.org> wrote:
> On 27 March 2015 at 15:52, Xunlei Pang <pang.xun...@linaro.org> wrote:
>> Hi Vincent,
>>
>> On 27 February 2015 at 23:54, Vincent Guittot
>> <vincent.guit...@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
Maybe I didn't make it clearly.
For example, CPU0~1 are SMT siblings, CPU2~CPU3 are another pair.
CPU0 is idle, others each has 1 task. Then according to this patch,
CPU2~CPU3(as one group) will be viewed as overloaded(CPU0~CPU1 as
local group, and group_has_capacity() returns true here), so the
balancer may initiate an active task moving. This is different from
the current code as SD_PREFER_SIBLING logic does. Is this problematic?
>
>>
>> -Xunlei
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