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SubjectRe: [PATCH v4] sched: Avoid unnecessary work in reweight_entity
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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 :-(

> 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);

> #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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