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SubjectRe: [PATCH 5/5] sched: make fix_small_imbalance work with asymmetric packing
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On Fri, 2010-04-09 at 16:21 +1000, Michael Neuling wrote:
> With the asymmetric packing infrastructure, fix_small_imbalance is
> causing idle higher threads to pull tasks off lower threads.
>
> This is being caused by an off-by-one error.
>
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> ---
> I'm not sure this is the right fix but without it, higher threads pull
> tasks off the lower threads, then the packing pulls it back down, etc
> etc and tasks bounce around constantly.

Would help if you expand upon the why/how it manages to get pulled up.

I can't immediately spot anything wrong with the patch, but then that
isn't my favourite piece of code either.. Suresh, any comments?

> ---
>
> kernel/sched_fair.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-2.6-ozlabs/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6-ozlabs.orig/kernel/sched_fair.c
> +++ linux-2.6-ozlabs/kernel/sched_fair.c
> @@ -2652,7 +2652,7 @@ static inline void fix_small_imbalance(s
> * SCHED_LOAD_SCALE;
> scaled_busy_load_per_task /= sds->busiest->cpu_power;
>
> - if (sds->max_load - sds->this_load + scaled_busy_load_per_task >=
> + if (sds->max_load - sds->this_load + scaled_busy_load_per_task >
> (scaled_busy_load_per_task * imbn)) {
> *imbalance = sds->busiest_load_per_task;
> return;



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