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SubjectRe: [PATCH 4/4] sched/fair: reduce busy load balance interval
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On 14/09/20 11:03, Vincent Guittot wrote:
> The busy_factor, which increases load balance interval when a cpu is busy,
> is set to 32 by default. This value generates some huge LB interval on
> large system like the THX2 made of 2 node x 28 cores x 4 threads.
> For such system, the interval increases from 112ms to 3584ms at MC level.
> And from 228ms to 7168ms at NUMA level.
>
> Even on smaller system, a lower busy factor has shown improvement on the
> fair distribution of the running time so let reduce it for all.
>

ISTR you mentioned taking this one step further and making
(interval * busy_factor) scale logarithmically with the number of CPUs to
avoid reaching outrageous numbers. Did you experiment with that already?

> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> kernel/sched/topology.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 1a84b778755d..a8477c9e8569 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1336,7 +1336,7 @@ sd_init(struct sched_domain_topology_level *tl,
> *sd = (struct sched_domain){
> .min_interval = sd_weight,
> .max_interval = 2*sd_weight,
> - .busy_factor = 32,
> + .busy_factor = 16,
> .imbalance_pct = 117,
>
> .cache_nice_tries = 0,

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