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SubjectRe: [PATCH] sched: improve smpnice load balancing when load per task imbalanced

* Peter Williams <pwil3058@bigpond.net.au> wrote:

> Problem:
>
> 2 CPU system: if the cpu-0 has two high priority and cpu-1 has one
> normal priority task, how can the current code detect this imbalance
> because imbalance will be always < busiest_load_per_task and max_load
> - this_load will be < 2 * busiest_load_per_task and pwr_move will be
> <= pwr_now.
>
> Solution:
>
> Modify the assessment of small imbalances to take into account the
> relative sizes of busiest_load_per_task and this_load_per_task. This
> is exploiting the fact that if the difference between the loads is
> greater than busiest_load_per_task and busiest_load_per_task is
> greater than this_load_per_task then moving busiest_load_per_task
> worth of load from busiest to this will be an improvement in the
> distribution of weighted load.
>
> Required patches:
>
> sched-prevent-high-load-weight-tasks-suppressing-balancing.patch
> sched-improve-stability-of-smpnice-load-balancing.patch
>
> Note: This patch makes no change to load balancing in the case where
> all tasks are nice==0.
>
> Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>

Acked-by: Ingo Molnar <mingo@elte.hu>

Ingo
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