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

[Ingo Molnar <mingo@elte.hu>]

* 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