Re: [RFC][PATCH 06/14] sched/fair: Move enqueue migrate handling

[Vincent Guittot]

On 12 May 2017 at 18:44, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> Move the entity migrate handling from enqueue_entity_load_avg() to
> update_load_avg(). This has two benefits:
>
>  - {en,de}queue_entity_load_avg() will become purely about managing
>    runnable_load
>
>  - we can avoid a double update_tg_load_avg() and reduce pressure on
>    the global tg->shares cacheline
>
> The reason we do this is so that we can change update_cfs_shares() to
> change both weight and (future) runnable_weight. For this to work we
> need to have the cfs_rq averages up-to-date (which means having done
> the attach), but we need the cfs_rq->avg.runnable_avg to not yet
> include the se's contribution (since se->on_rq == 0).
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Acked-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

> ---
>  kernel/sched/fair.c |   70 ++++++++++++++++++++++++++--------------------------
>  1 file changed, 36 insertions(+), 34 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3418,34 +3418,6 @@ update_cfs_rq_load_avg(u64 now, struct c
>         return decayed || removed_load;
>  }
>
> -/*
> - * Optional action to be done while updating the load average
> - */
> -#define UPDATE_TG      0x1
> -#define SKIP_AGE_LOAD  0x2
> -
> -/* Update task and its cfs_rq load average */
> -static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> -{
> -       u64 now = cfs_rq_clock_task(cfs_rq);
> -       struct rq *rq = rq_of(cfs_rq);
> -       int cpu = cpu_of(rq);
> -       int decayed;
> -
> -       /*
> -        * Track task load average for carrying it to new CPU after migrated, and
> -        * track group sched_entity load average for task_h_load calc in migration
> -        */
> -       if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
> -               __update_load_avg_se(now, cpu, cfs_rq, se);
> -
> -       decayed  = update_cfs_rq_load_avg(now, cfs_rq, true);
> -       decayed |= propagate_entity_load_avg(se);
> -
> -       if (decayed && (flags & UPDATE_TG))
> -               update_tg_load_avg(cfs_rq, 0);
> -}
> -
>  /**
>   * attach_entity_load_avg - attach this entity to its cfs_rq load avg
>   * @cfs_rq: cfs_rq to attach to
> @@ -3486,17 +3458,46 @@ static void detach_entity_load_avg(struc
>         cfs_rq_util_change(cfs_rq);
>  }
>
> +/*
> + * Optional action to be done while updating the load average
> + */
> +#define UPDATE_TG      0x1
> +#define SKIP_AGE_LOAD  0x2
> +#define DO_ATTACH      0x4
> +
> +/* Update task and its cfs_rq load average */
> +static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> +{
> +       u64 now = cfs_rq_clock_task(cfs_rq);
> +       struct rq *rq = rq_of(cfs_rq);
> +       int cpu = cpu_of(rq);
> +       int decayed;
> +
> +       /*
> +        * Track task load average for carrying it to new CPU after migrated, and
> +        * track group sched_entity load average for task_h_load calc in migration
> +        */
> +       if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
> +               __update_load_avg_se(now, cpu, cfs_rq, se);
> +
> +       decayed  = update_cfs_rq_load_avg(now, cfs_rq, true);
> +       decayed |= propagate_entity_load_avg(se);
> +
> +       if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
> +
> +               attach_entity_load_avg(cfs_rq, se);
> +               update_tg_load_avg(cfs_rq, 0);
> +
> +       } else if (decayed && (flags & UPDATE_TG))
> +               update_tg_load_avg(cfs_rq, 0);
> +}
> +
>  /* Add the load generated by se into cfs_rq's load average */
>  static inline void
>  enqueue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
>         cfs_rq->runnable_load_avg += se->avg.load_avg;
>         cfs_rq->runnable_load_sum += se_weight(se) * se->avg.load_sum;
> -
> -       if (!se->avg.last_update_time) {
> -               attach_entity_load_avg(cfs_rq, se);
> -               update_tg_load_avg(cfs_rq, 0);
> -       }
>  }
>
>  /* Remove the runnable load generated by se from cfs_rq's runnable load average */
> @@ -3586,6 +3587,7 @@ update_cfs_rq_load_avg(u64 now, struct c
>
>  #define UPDATE_TG      0x0
>  #define SKIP_AGE_LOAD  0x0
> +#define DO_ATTACH      0x0
>
>  static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
>  {
> @@ -3740,7 +3742,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
>          *     its group cfs_rq
>          *   - Add its new weight to cfs_rq->load.weight
>          */
> -       update_load_avg(cfs_rq, se, UPDATE_TG);
> +       update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH);
>         enqueue_entity_load_avg(cfs_rq, se);
>         update_cfs_shares(se);
>         account_entity_enqueue(cfs_rq, se);
>
>