Re: [PATCH 3/4 v2] sched/fair: minimize concurrent LBs between domain level

[Valentin Schneider]

On 21/09/20 08:24, Vincent Guittot wrote:
> sched domains tend to trigger simultaneously the load balance loop but
> the larger domains often need more time to collect statistics. This
> slowness makes the larger domain trying to detach tasks from a rq whereas
> tasks already migrated somewhere else at a sub-domain level. This is not
> a real problem for idle LB because the period of smaller domains will
> increase with its CPUs being busy and this will let time for higher ones
> to pulled tasks. But this becomes a problem when all CPUs are already busy
> because all domains stay synced when they trigger their LB.
>
> A simple way to minimize simultaneous LB of all domains is to decrement the
> the busy interval by 1 jiffies. Because of the busy_factor, the interval of
> larger domain will not be a multiple of smaller ones anymore.
>
> Reviewed-by: Phil Auld <pauld@xxxxxxxxxx>
> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

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