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

[Alex Shi]

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.

Thanks for your question, Vincent!
the runnable_avg_period and runnable_avg_sum, only updated in
__update_entity_runnable_avg().
Yes, I didn't see some locks to ensure the coherent of them. but they
are updated closely, and it is not big deal even a little incorrect to
their value. These data are collected periodically, don't need very very
precise at every time.
Am I right? :)

-- 
Thanks Alex
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