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SubjectRe: [PATCH 08/18] sched: consider runnable load average in move_tasks
On 12/12/2012 12:41 PM, Preeti U Murthy wrote:
> Hi Alex,
> On 12/10/2012 01:52 PM, Alex Shi 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@intel.com>
>> ---
>> kernel/sched/fair.c | 11 ++++++++++-
>> 1 files changed, 10 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 6d893a6..bbb069c 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3741,6 +3741,15 @@ 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;
> ^^^^^^^^^^^^
> This might result in an overflow,considering you are multiplying two 32
> bit integers.Below is how this is handled in
> __update_task_entity_contrib in kernel/sched/fair.c
>
> u32 contrib;
> /* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
> contrib = se->avg.runnable_avg_sum * scale_load_down(se->load.weight);
> contrib /= (se->avg.runnable_avg_period + 1);
> se->avg.load_avg_contrib = scale_load(contrib);

scale_load_down is do nothing.
>
> Also why can't p->se.load_avg_contrib be used directly? as a return
> value for task_h_load_avg? since this is already updated in
> update_task_entity_contrib and update_group_entity_contrib.

No, only non task entity goes to update_group_entity_contrib. not task
entity.


>> +}
>> +
>> /*
>> * move_tasks tries to move up to imbalance weighted load from busiest to
>> * this_rq, as part of a balancing operation within domain "sd".
>> @@ -3776,7 +3785,7 @@ 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;
>>
>
> Regards
> Preeti U Murthy
>



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