On 1 April 2015 at 05:37, Xunlei Pang <[email protected]> wrote: > Hi Vincent, > > On 27 March 2015 at 23:59, Vincent Guittot <[email protected]> wrote: >> On 27 March 2015 at 15:52, Xunlei Pang <[email protected]> wrote: >>> Hi Vincent, >>> >>> On 27 February 2015 at 23:54, Vincent Guittot >>> <[email protected]> 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?
IMHO, it's not problematic, It's worth triggering a load balance if there is an imbalance between the 2 groups (as an example CPU0~1 has one low nice prio task but CPU1~2 have 2 high nice prio tasks) so the decision will be done when calculating the imbalance Vincent > >> >>> >>> -Xunlei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
