Re: [PATCH 2/3] sched/fair: trigger asym_packing during idle load balance

[Valentin Schneider <valentin.schneider@arm.com>]

On 20/12/2018 07:55, Vincent Guittot wrote:
> newly idle load balance is not always triggered when a cpu becomes idle.
> This prevent the scheduler to get a chance to migrate task for asym packing.
> Enable active migration because of asym packing during idle load balance too.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 9b31247..487c73e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8853,7 +8853,7 @@ static int need_active_balance(struct lb_env *env)
>  {
>  	struct sched_domain *sd = env->sd;
>  
> -	if (env->idle == CPU_NEWLY_IDLE) {
> +	if (env->idle != CPU_NOT_IDLE) {
>  
>  		/*
>  		 * ASYM_PACKING needs to force migrate tasks from busy but
> 

Regarding just extending the condition to include idle balance:

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>


As in the previous thread, I'll still argue that if you want to *reliably*
exploit newidle balances to do asym packing active balancing, you should
add some logic to raise rq->rd->overload when we notice some asym packing
could be done, so that it can be leveraged by a higher-priority CPU doing
a newidle balance.

Otherwise the few newidle asym-packing active balances you'll get will be
due to somewhat random luck because we happened to set that overload flag
at some point.