Messages in this thread | | | Date | Sat, 18 Feb 2012 09:43:55 +0800 | From | Michael Wang <> | Subject | Re: [PATCH v5] sched: Avoid unnecessary work in reweight_entity |
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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)
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