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SubjectRe: [PATCH v4] sched: Avoid unnecessary work in reweight_entity
Hi, Peter

Thanks for your reply.

On 02/16/2012 10:29 PM, Peter Zijlstra wrote:

> On Thu, 2012-02-16 at 22:14 +0800, Michael Wang wrote:
>> From: Michael Wang <wangyun@linux.vnet.ibm.com>
>>
>> In original code, using account_entity_dequeue and account_entity_enqueue
>> as a pair will do some work unnecessary, such like remove node from list
>> and add it back again immediately.
>>
>> And because there are no really enqueue and dequeue happen here, it is not
>> suitable to use account_entity_dequeue and account_entity_enqueue here.
>>
>> This patch combine the work of them in order to save time.
>
> And yet no numbers on how much it saves :-(
>


That's right...
Actually I don't know how to prove the performance improvement, please
give me some suggestion and I will do it :)

>> Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
>> ---
>> kernel/sched/fair.c | 27 +++++++++++++++++++++------
>> kernel/sched/sched.h | 8 ++++++++
>> 2 files changed, 29 insertions(+), 6 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 7c6414f..fda63ec 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -777,16 +777,28 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
>> */
>>
>> #if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
>> -static void
>> +static inline void
>> add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
>> {
>> cfs_rq->task_weight += weight;
>> }
>> +
>> +static inline void
>> +sub_add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long sub, unsigned long add)
>> +{
>> + cfs_rq->task_weight -= sub;
>> + cfs_rq->task_weight += add;
>> +}
>
> This is pointless, just use: add_cfs_task_weight(cfs_rq, add - sub);
>


Sorry for the silly code, v5 will correct it and all the issues mentioned below.

Regards,
Michael Wang

>> #else
>> static inline void
>> add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
>> {
>> }
>> +
>> +static inline void
>> +sub_add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long sub, unsigned long add)
>> +{
>> +}
>> #endif
>>
>> static void
>> @@ -938,6 +950,7 @@ static inline void update_entity_shares_tick(struct cfs_rq *cfs_rq)
>> {
>> }
>> # endif /* CONFIG_SMP */
>> +
>> static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>> unsigned long weight)
>> {
>> @@ -945,13 +958,15 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>> /* commit outstanding execution time */
>> if (cfs_rq->curr == se)
>> update_curr(cfs_rq);
>> - account_entity_dequeue(cfs_rq, se);
>> + update_load_sub_add(&cfs_rq->load, se->load.weight, weight);
>> + if (!parent_entity(se)) {
>> + update_load_sub_add(&rq_of(cfs_rq)->load, se->load.weight, weight);
>
> same here:
> update_load_add(&rq_of(cfs_rq)->load, weight - se->load.weight);
>
> Also superfluous use of curly-braces here.
>
>> + }
>> + if (entity_is_task(se)) {
>> + sub_add_cfs_task_weight(cfs_rq, se->load.weight, weight);
>> + }
>
> idem.
>
>> }
>> -
>> update_load_set(&se->load, weight);
>> -
>> - if (se->on_rq)
>> - account_entity_enqueue(cfs_rq, se);
>> }
>>
>> static void update_cfs_shares(struct cfs_rq *cfs_rq)
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index 98c0c26..ec4430f 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -779,6 +779,14 @@ static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
>> lw->inv_weight = 0;
>> }
>>
>> +static inline void update_load_sub_add(struct load_weight *lw, unsigned long dec,
>> + unsigned long inc)
>> +{
>> + lw->weight -= dec;
>> + lw->weight += inc;
>> + lw->inv_weight = 0;
>> +}
>
> again, pointless stuff.
>
>> static inline void update_load_set(struct load_weight *lw, unsigned long w)
>> {
>> lw->weight = w;
>




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