lkml.org 
[lkml]   [2015]   [Apr]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v10 08/11] sched: replace capacity_factor by usage
From
Hi Vincent,

On 1 April 2015 at 17:06, Vincent Guittot <vincent.guittot@linaro.org> wrote:
> On 1 April 2015 at 05:37, Xunlei Pang <pang.xunlei@linaro.org> wrote:
>> Hi Vincent,
>>
>> On 27 March 2015 at 23:59, Vincent Guittot <vincent.guittot@linaro.org> wrote:
>>> 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
>>
>> 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

Yes, but assuming the balancer calculated some imbalance, after moving
like CPU0~CPU1 have 1 low prio task and 1 high prio task, CPU2~CPU3
have 1 high piro task, seems it does no good because there's only 1
task per CPU after all.

So, is code below better( we may have more than 2 SMT siblings, like
Broadcom XLP processor having 4 SMT per core)?
if (prefer_sibling && sds->local &&
group_has_capacity(env, &sds->local_stat) &&
(sgs->sum_nr_running > sds->local_stat.sum_nr_running + 1)) {
sgs->group_no_capacity = 1;
sgs->group_type = group_overloaded;
}

Thanks,
-Xunlei


\
 
 \ /
  Last update: 2015-04-01 17:21    [W:0.352 / U:2.200 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site