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Message-ID: <26a71d5c-9a4a-4064-8155-a14126a654f8@gmail.com>
Date: Fri, 3 Nov 2023 22:01:55 +0800
From: Yiwei Lin <s921975628@...il.com>
To: Abel Wu <wuyun.abel@...edance.com>, mingo@...hat.com,
peterz@...radead.org
Cc: vincent.guittot@...aro.org, dietmar.eggemann@....com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] sched/fair: Track current se's EEVDF parameters
On 11/3/23 14:45, Abel Wu wrote:
> On 11/2/23 10:20 PM, Yiwei Lin Wrote:
>> After dequeuing the current-picked scheduling entity with
>> `__dequeue_entity`, its contribution to the EEVDF parameters
>> cfs_rq->avg_vruntime and cfs_rq->avg_load are also removed.
>> Because these should in fact be considered for the EEVDF algorithm,
>> we took curr as the special case and inserted back the contributions
>> when requests for cfs_rq->avg_vruntime and cfs_rq->avg_load.
>>
>> Functions like `entity_eligible` which is called insied a loop may
>> therefore recalculate these statistics repeatly and require more effort.
>> Instead, we could just avoid to remove these statistics from
>> cfs_rq->avg_vruntime and cfs_rq->avg_load directly.
>>
>> Signed-off-by: Yiwei Lin <s921975628@...il.com>
>> ---
>> kernel/sched/fair.c | 39 +++++++++++----------------------------
>> 1 file changed, 11 insertions(+), 28 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 876798824..a10a73603 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -655,17 +655,9 @@ void avg_vruntime_update(struct cfs_rq *cfs_rq,
>> s64 delta)
>> */
>> u64 avg_vruntime(struct cfs_rq *cfs_rq)
>> {
>> - struct sched_entity *curr = cfs_rq->curr;
>> s64 avg = cfs_rq->avg_vruntime;
>> long load = cfs_rq->avg_load;
>> - if (curr && curr->on_rq) {
>> - unsigned long weight = scale_load_down(curr->load.weight);
>> -
>> - avg += entity_key(cfs_rq, curr) * weight;
>> - load += weight;
>> - }
>> -
>> if (load) {
>> /* sign flips effective floor / ceil */
>> if (avg < 0)
>> @@ -722,17 +714,9 @@ static void update_entity_lag(struct cfs_rq
>> *cfs_rq, struct sched_entity *se)
>> */
>> int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
>> {
>> - struct sched_entity *curr = cfs_rq->curr;
>> s64 avg = cfs_rq->avg_vruntime;
>> long load = cfs_rq->avg_load;
>> - if (curr && curr->on_rq) {
>> - unsigned long weight = scale_load_down(curr->load.weight);
>> -
>> - avg += entity_key(cfs_rq, curr) * weight;
>> - load += weight;
>> - }
>> -
>> return avg >= entity_key(cfs_rq, se) * load;
>> }
>> @@ -821,11 +805,12 @@ static void __enqueue_entity(struct cfs_rq
>> *cfs_rq, struct sched_entity *se)
>> __entity_less, &min_deadline_cb);
>> }
>> -static void __dequeue_entity(struct cfs_rq *cfs_rq, struct
>> sched_entity *se)
>> +static void __dequeue_entity(struct cfs_rq *cfs_rq, struct
>> sched_entity *se, bool on_rq)
>
> Please don't add such complexity. Since avg_vruntime includes the whole
> cfs_rq after this change, you can simply avg_vruntime_add() when doing
> enqueue_entity() and avg_vruntime_sub() in dequeue_entity().
>
Right. I should consider that we'll also use __enqueue_entity to put
back the 'curr', and
avg_vruntime_add() when doing enqueue_entity() and avg_vruntime_sub() in
dequeue_entity()
as you mentioned could not only simplify the implementation but also
address to this issue.
I'll fix it.
>> {
>> rb_erase_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
>> &min_deadline_cb);
>> - avg_vruntime_sub(cfs_rq, se);
>> + if (!on_rq)
>> + avg_vruntime_sub(cfs_rq, se);
>> }
>> struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
>> @@ -1137,6 +1122,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
>> struct sched_entity *curr = cfs_rq->curr;
>> u64 now = rq_clock_task(rq_of(cfs_rq));
>> u64 delta_exec;
>> + u64 delta_fair;
>> if (unlikely(!curr))
>> return;
>> @@ -1158,7 +1144,9 @@ static void update_curr(struct cfs_rq *cfs_rq)
>> curr->sum_exec_runtime += delta_exec;
>> schedstat_add(cfs_rq->exec_clock, delta_exec);
>> - curr->vruntime += calc_delta_fair(delta_exec, curr);
>> + delta_fair = calc_delta_fair(delta_exec, curr);
>> + curr->vruntime += delta_fair;
>> + cfs_rq->avg_vruntime += delta_fair *
>> scale_load_down(curr->load.weight);
>
> What if curr->load.weight changes in this time slice?
The change on reweight_entity now don't separate curr and other
entities. If curr->load.weight is changed,
reweight_entity will do:
1. update_curr() to account the latest contribution of vruntime with old
weight.
2. avg_vruntime_sub() to remove the curr vruntime with old weight
3. avg_vruntime_add() to insert the curr vruntime with new weight
Although step1 and step2 could be merged together when re-weighting the
curr entity, but it
seems just find to general implement reweight_entity.
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