If a se is on_rq when reweighting entity, all we need should be
updating the load of cfs_rq, other dequeue/enqueue works could be
redundant, such as,
* account_numa_dequeue/account_numa_enqueue
* list_del/list_add from/into cfs_tasks
* nr_running--/nr_running++
Just simplfy the work. Could be helpful for the hot path.
Signed-off-by: Jiang Biao <[email protected]>
---
kernel/sched/fair.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 04fa8dbcfa4d..18a8fc7bd0de 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3086,7 +3086,7 @@ 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(&cfs_rq->load, se->load.weight);
}
dequeue_load_avg(cfs_rq, se);
@@ -3102,7 +3102,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
enqueue_load_avg(cfs_rq, se);
if (se->on_rq)
- account_entity_enqueue(cfs_rq, se);
+ update_load_add(&cfs_rq->load, se->load.weight);
}
--
2.21.0
On 04/08/2020 09:12, Jiang Biao wrote:
> If a se is on_rq when reweighting entity, all we need should be
> updating the load of cfs_rq, other dequeue/enqueue works could be
> redundant, such as,
> * account_numa_dequeue/account_numa_enqueue
> * list_del/list_add from/into cfs_tasks
> * nr_running--/nr_running++
I think this could make sense. Have you spotted a code path where this
gives you a change?
I guess only for a task on the rq, so: entity_is_task(se) && se->on_rq
> Just simplfy the work. Could be helpful for the hot path.
IMHO hotpath is update_cfs_group() -> reweight_entity() but this is only
called for '!entity_is_task(se)'.
See
3290 if (!gcfs_rq)
3291 return;
in update_cfs_group().
The 'entity_is_task(se)' case is
set_load_weight(struct task_struct *p, ...) -> reweight_task(p, ...) ->
reweight_entity(..., &p->se, ...)
but here !se->on_rq.
> Signed-off-by: Jiang Biao <[email protected]>
> ---
> kernel/sched/fair.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 04fa8dbcfa4d..18a8fc7bd0de 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3086,7 +3086,7 @@ 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(&cfs_rq->load, se->load.weight);
> }
> dequeue_load_avg(cfs_rq, se);
>
> @@ -3102,7 +3102,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>
> enqueue_load_avg(cfs_rq, se);
> if (se->on_rq)
> - account_entity_enqueue(cfs_rq, se);
> + update_load_add(&cfs_rq->load, se->load.weight);
>
> }
> On Aug 6, 2020, at 12:21 AM, Dietmar Eggemann <[email protected]> wrote:
>
> On 04/08/2020 09:12, Jiang Biao wrote:
>> If a se is on_rq when reweighting entity, all we need should be
>> updating the load of cfs_rq, other dequeue/enqueue works could be
>> redundant, such as,
>> * account_numa_dequeue/account_numa_enqueue
>> * list_del/list_add from/into cfs_tasks
>> * nr_running--/nr_running++
>
> I think this could make sense. Have you spotted a code path where this
> gives you a change?
>
> I guess only for a task on the rq, so: entity_is_task(se) && se->on_rq
Yes, you're right. No other code path I spotted except what you list below.
>
>> Just simplfy the work. Could be helpful for the hot path.
>
> IMHO hotpath is update_cfs_group() -> reweight_entity() but this is only
> called for '!entity_is_task(se)'.
>
> See
>
> 3290 if (!gcfs_rq)
> 3291 return;
>
> in update_cfs_group().
Yes, It is.
But *nr_running--/nr_running++* works are still redundant for
‘!entity_is_task(se)' hot path. :)
Besides, I guess we could simplify the logic and make it cleaner and
more readable with this patch.
If it could make sense to you, would you mind if I resend the patch
with the commit log amended?
>
> The 'entity_is_task(se)' case is
>
> set_load_weight(struct task_struct *p, ...) -> reweight_task(p, ...) ->
> reweight_entity(..., &p->se, ...)
>
> but here !se->on_rq.
Yes, indeed.
Thanks a lot for your comments.
Regards,
Jiang
>
>> Signed-off-by: Jiang Biao <[email protected]>
>> ---
>> kernel/sched/fair.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 04fa8dbcfa4d..18a8fc7bd0de 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3086,7 +3086,7 @@ 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(&cfs_rq->load, se->load.weight);
>> }
>> dequeue_load_avg(cfs_rq, se);
>>
>> @@ -3102,7 +3102,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>>
>> enqueue_load_avg(cfs_rq, se);
>> if (se->on_rq)
>> - account_entity_enqueue(cfs_rq, se);
>> + update_load_add(&cfs_rq->load, se->load.weight);
>>
>> }
>
On 06/08/2020 04:42, benbjiang(蒋彪) wrote:
>
>
>> On Aug 6, 2020, at 12:21 AM, Dietmar Eggemann <[email protected]> wrote:
>>
>> On 04/08/2020 09:12, Jiang Biao wrote:
>>> If a se is on_rq when reweighting entity, all we need should be
>>> updating the load of cfs_rq, other dequeue/enqueue works could be
>>> redundant, such as,
>>> * account_numa_dequeue/account_numa_enqueue
>>> * list_del/list_add from/into cfs_tasks
>>> * nr_running--/nr_running++
>>
>> I think this could make sense. Have you spotted a code path where this
>> gives you a change?
>>
>> I guess only for a task on the rq, so: entity_is_task(se) && se->on_rq
> Yes, you're right. No other code path I spotted except what you list below.
>
>>
>>> Just simplfy the work. Could be helpful for the hot path.
>>
>> IMHO hotpath is update_cfs_group() -> reweight_entity() but this is only
>> called for '!entity_is_task(se)'.
>>
>> See
>>
>> 3290 if (!gcfs_rq)
>> 3291 return;
>>
>> in update_cfs_group().
> Yes, It is.
> But *nr_running--/nr_running++* works are still redundant for
> ‘!entity_is_task(se)' hot path. :)
True.
> Besides, I guess we could simplify the logic and make it cleaner and
> more readable with this patch.
Yes.
> If it could make sense to you, would you mind if I resend the patch
> with the commit log amended?
LGTM so why not?
>> The 'entity_is_task(se)' case is
>>
>> set_load_weight(struct task_struct *p, ...) -> reweight_task(p, ...) ->
>> reweight_entity(..., &p->se, ...)
>>
>> but here !se->on_rq.
> Yes, indeed.
[...]