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SubjectRe: [PATCH v3 08/10] sched/fair: use utilization to select misfit task
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On 19/09/2019 08:33, Vincent Guittot wrote:
> utilization is used to detect a misfit task but the load is then used to
> select the task on the CPU which can lead to select a small task with
> high weight instead of the task that triggered the misfit migration.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> Acked-by: Valentin Schneider <valentin.schneider@arm.com>
> ---
> kernel/sched/fair.c | 10 ++--------
> 1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a7c8ee6..acca869 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7429,14 +7429,8 @@ static int detach_tasks(struct lb_env *env)
> break;
>
> case migrate_misfit:
> - load = task_h_load(p);
> -
> - /*
> - * utilization of misfit task might decrease a bit
> - * since it has been recorded. Be conservative in the
> - * condition.
> - */
> - if (load < env->imbalance)
> + /* This is not a misfit task */
> + if (task_fits_capacity(p, capacity_of(env->src_cpu)))
> goto next;
>
> env->imbalance = 0;
>

Following my comment in [1], if you can't squash that in patch 04 then
perhaps you could add that to this change:

---
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1fac444a4831..d09ce304161d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8343,7 +8343,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
if (busiest->group_type == group_misfit_task) {
/* Set imbalance to allow misfit task to be balanced. */
env->balance_type = migrate_misfit;
- env->imbalance = busiest->group_misfit_task_load;
+ env->imbalance = 1;
return;
}

---
Reason being we don't care about the load (anymore), we just want a nonzero
imbalance value, so might as well assign something static.

[1]: https://lore.kernel.org/r/74bb33d7-3ba4-aabe-c7a2-3865d5759281@arm.com

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