From: Jiang Biao <[email protected]>
If a se is on_rq when reweighting entity, all we need should be
updating the load of cfs_rq, other dequeue/enqueue work could be
redundant, such as,
* nr_running--/nr_running++
Even though the following dequeue/enqueue path would never be reached
* account_numa_dequeue/account_numa_enqueue
* list_del/list_add from/into cfs_tasks
but it could be a little confusing.
Simplifying the logic could be helpful to reduce a litte overhead for
hot path, and make it cleaner and more readable.
Signed-off-by: Jiang Biao <[email protected]>
---
v2<-v1:
- Amend the commit log.
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 06/08/2020 18:14, Jiang Biao wrote:
> From: Jiang Biao <[email protected]>
>
> If a se is on_rq when reweighting entity, all we need should be
> updating the load of cfs_rq, other dequeue/enqueue work could be
> redundant, such as,
> * nr_running--/nr_running++
>
> Even though the following dequeue/enqueue path would never be reached
> * account_numa_dequeue/account_numa_enqueue
> * list_del/list_add from/into cfs_tasks
> but it could be a little confusing.
>
> Simplifying the logic could be helpful to reduce a litte overhead for
> hot path, and make it cleaner and more readable.
LGTM. I guess you have to resend it w/o the RFC tag.
Maybe you can rework the patch header a little?
Something like this:
The code in reweight_entity() can be simplified.
For a sched entity on the rq, the entity accounting can be replaced by
cfs_rq instantaneous load updates currently called from within the
entity accounting.
Even though an entity on the rq can't represent a task in
reweight_entity() (a task is always dequeued before calling this
function) and so the numa task accounting and the rq->cfs_tasks list
management of the entity accounting are never called, the redundant
cfs_rq->nr_running decrement/increment will be avoided.
>
> Signed-off-by: Jiang Biao <[email protected]>
> ---
> v2<-v1:
> - Amend the commit log.
>
> 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);
>
> }
Hi,
> On Aug 11, 2020, at 5:50 PM, Dietmar Eggemann <[email protected]> wrote:
>
> On 06/08/2020 18:14, Jiang Biao wrote:
>> From: Jiang Biao <[email protected]>
>>
>> If a se is on_rq when reweighting entity, all we need should be
>> updating the load of cfs_rq, other dequeue/enqueue work could be
>> redundant, such as,
>> * nr_running--/nr_running++
>>
>> Even though the following dequeue/enqueue path would never be reached
>> * account_numa_dequeue/account_numa_enqueue
>> * list_del/list_add from/into cfs_tasks
>> but it could be a little confusing.
>>
>> Simplifying the logic could be helpful to reduce a litte overhead for
>> hot path, and make it cleaner and more readable.
>
> LGTM. I guess you have to resend it w/o the RFC tag.
Will do soon.
>
> Maybe you can rework the patch header a little?
>
> Something like this:
>
> The code in reweight_entity() can be simplified.
>
> For a sched entity on the rq, the entity accounting can be replaced by
> cfs_rq instantaneous load updates currently called from within the
> entity accounting.
>
> Even though an entity on the rq can't represent a task in
> reweight_entity() (a task is always dequeued before calling this
> function) and so the numa task accounting and the rq->cfs_tasks list
> management of the entity accounting are never called, the redundant
> cfs_rq->nr_running decrement/increment will be avoided.
That’s a much better. I’ll pick the header if you don’t mind. :)
Thanks a lot for your kindly reply and detailed explanation.
Regards,
Jiang
>
>>
>> Signed-off-by: Jiang Biao <[email protected]>
>> ---
>> v2<-v1:
>> - Amend the commit log.
>>
>> 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);
>>
>> }