lkml.org 
[lkml]   [2012]   [Feb]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v5] sched: Avoid unnecessary work in reweight_entity
Hi, Peter

This is the v5, any I found there will be the case that weight == se->load.weight
in reweight_entity(very often according to the log), so I add the check point.

And I try to use perf to see whether it can help to prove the improvement, but get:

invalid or unsupported event: 'sched:sched_switch'

when use command "perf sched record".

And also someone told me that even use perf sched may not be able to prove anything
because what I do may only help improve little performance which can not be easily
detected :(

So may be we can prove this patch's performance improvement logically, the summary is:

1. reduce times to check "se->on" from 2 to 1.
2. reduce times to check "parent_entity(se)" from 2 to 1.
3. reduce times to check "entity_is_task(se)" from 2 to 1.
4. reduce times to set "cfs_rq->load.inv_weight" from 4 to 2.
5. reduce times to set "rq_of(cfs_rq)->load.inv_weight" from 2 to 1.
6. no need to use "list_add(&se->group_node, &cfs_rq->tasks);" any more.
7. no need to use "list_del_init(&se->group_node);" any more.
8. no need to do "cfs_rq->nr_running++" and "cfs_rq->nr_running--" any more.

above summary is already in previous mail, any for v5, we get one more:

9. do nothing if the new weight is same to the old weight.

And as reight_entity is invoked very often, I think this patch can do some help to the
performance, although there are no numbers, we can prove it logically :)

Best regards,
Michael Wang

On 02/17/2012 02:03 PM, 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.
>
> since v1:
> Add more description.
> Mark add_cfs_task_weight as inline.
> correct useless and wrong code.
> Add check point for the case there is no change on weight.
>
> Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
> ---
> kernel/sched/fair.c | 16 ++++++++++------
> 1 files changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 7c6414f..20aa355 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -777,7 +777,7 @@ 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;
> @@ -938,20 +938,24 @@ 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)
> {
> + if (weight == se->load.weight)
> + return;
> +
> if (se->on_rq) {
> /* commit outstanding execution time */
> if (cfs_rq->curr == se)
> update_curr(cfs_rq);
> - account_entity_dequeue(cfs_rq, se);
> + update_load_add(&cfs_rq->load, weight - se->load.weight);
> + if (!parent_entity(se))
> + update_load_add(&rq_of(cfs_rq)->load, weight - se->load.weight);
> + if (entity_is_task(se))
> + add_cfs_task_weight(cfs_rq, weight - se->load.weight);
> }
> -
> 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)




\
 
 \ /
  Last update: 2012-02-18 02:47    [from the cache]
©2003-2011 Jasper Spaans