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SubjectRe: [PATCH v2] sched/fair: Remove setting task's se->runnable_weight during PELT update
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Hi,

On 08/03/2018 07:05 AM, Dietmar Eggemann wrote:
> A CFS (SCHED_OTHER, SCHED_BATCH or SCHED_IDLE policy) task's
> se->runnable_weight must always be in sync with its se->load.weight.
>
> se->runnable_weight is set to se->load.weight when the task is
> forked (init_entity_runnable_average()) or reniced (reweight_entity()).
>
> There are two cases in set_load_weight() which since they currently only
> set se->load.weight could lead to a situation in which se->load.weight
> is different to se->runnable_weight for a CFS task:
>
> (1) A task switches to SCHED_IDLE.
>
> (2) A SCHED_FIFO, SCHED_RR or SCHED_DEADLINE task which has been reniced
> (during which only its static priority gets set) switches to
> SCHED_OTHER or SCHED_BATCH.
>
> Set se->runnable_weight to se->load.weight in these two cases to prevent
> this. This eliminates the need to explicitly set it to se->load.weight
> during PELT updates in the CFS scheduler fastpath.
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> ---
>
> Changes v1->v2:
> - Rebased on latest tip/sched/core
>
> This patch has been tested w/ appropriate BUG_ON()'s in
> __update_load_avg_blocked_se() and __update_load_avg_se() on an Ubuntu
> 18.04 desktop.
>
> kernel/sched/core.c | 2 ++
> kernel/sched/pelt.c | 6 ------
> 2 files changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index deafa9fe602b..2a08418db3d1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -701,6 +701,7 @@ static void set_load_weight(struct task_struct *p, bool update_load)
> if (idle_policy(p->policy)) {
> load->weight = scale_load(WEIGHT_IDLEPRIO);
> load->inv_weight = WMULT_IDLEPRIO;
> + p->se.runnable_weight = load->weight;
> return;
> }
>
> @@ -713,6 +714,7 @@ static void set_load_weight(struct task_struct *p, bool update_load)
> } else {
> load->weight = scale_load(sched_prio_to_weight[prio]);
> load->inv_weight = sched_prio_to_wmult[prio];
> + p->se.runnable_weight = load->weight;
> }
> }
>
> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> index 35475c0c5419..d0016b16d23a 100644
> --- a/kernel/sched/pelt.c
> +++ b/kernel/sched/pelt.c
> @@ -269,9 +269,6 @@ ___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runna
>
> int __update_load_avg_blocked_se(u64 now, int cpu, struct sched_entity *se)
> {
> - if (entity_is_task(se))
> - se->runnable_weight = se->load.weight;
> -
> if (___update_load_sum(now, cpu, &se->avg, 0, 0, 0)) {
> ___update_load_avg(&se->avg, se_weight(se), se_runnable(se));
> return 1;
> @@ -282,9 +279,6 @@ int __update_load_avg_blocked_se(u64 now, int cpu, struct sched_entity *se)
>
> int __update_load_avg_se(u64 now, int cpu, struct cfs_rq *cfs_rq, struct sched_entity *se)
> {
> - if (entity_is_task(se))
> - se->runnable_weight = se->load.weight;
> -
> if (___update_load_sum(now, cpu, &se->avg, !!se->on_rq, !!se->on_rq,
> cfs_rq->curr == se)) {
>
>

Is there anything else I should do for this patch ?

Thanks,

-- Dietmar

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