Re: [patch v3 6/8] sched: consider runnable load average in move_tasks

[Vincent Guittot]

On 10 April 2013 08:07, Michael Wang <wangyun@xxxxxxxxxxxxxxxxxx> wrote:
> On 04/09/2013 03:08 PM, Vincent Guittot wrote:
>> On 2 April 2013 05:23, Alex Shi <alex.shi@xxxxxxxxx> wrote:
>>> Except using runnable load average in background, move_tasks is also
>>> the key functions in load balance. We need consider the runnable load
>>> average in it in order to the apple to apple load comparison.
>>>
>>> Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx>
>>> ---
>>>  kernel/sched/fair.c | 11 ++++++++++-
>>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index 1f9026e..bf4e0d4 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -3966,6 +3966,15 @@ static unsigned long task_h_load(struct task_struct *p);
>>>
>>>  static const unsigned int sched_nr_migrate_break = 32;
>>>
>>> +static unsigned long task_h_load_avg(struct task_struct *p)
>>> +{
>>> +       u32 period = p->se.avg.runnable_avg_period;
>>> +       if (!period)
>>> +               return 0;
>>> +
>>> +       return task_h_load(p) * p->se.avg.runnable_avg_sum / period;
>>
>> How do you ensure that runnable_avg_period and runnable_avg_sum are
>> coherent ? an update of the statistic can occur in the middle of your
>> sequence.
>
> Hi, Vincent
>
> Don't we have the 'rq->lock' to protect it?
>
> move_tasks() was invoked with double locked, for all the se on src and
> dst rq, no update should happen, isn't it?

you're right, the double lock protect against concurrent access my
remark doesn't apply here

Regards,
Vincent

>
> Regards,
> Michael Wang
>
>>
>> Vincent
>>
>>> +}
>>> +
>>>  /*
>>>   * move_tasks tries to move up to imbalance weighted load from busiest to
>>>   * this_rq, as part of a balancing operation within domain "sd".
>>> @@ -4001,7 +4010,7 @@ static int move_tasks(struct lb_env *env)
>>>                 if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
>>>                         goto next;
>>>
>>> -               load = task_h_load(p);
>>> +               load = task_h_load_avg(p);
>>>
>>>                 if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
>>>                         goto next;
>>> --
>>> 1.7.12
>>>
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