Re: [PATCH] timers/migration: Temporarily disable per capacity hierarchies

[Christian Loehle <christian.loehle@arm.com>]

On 6/9/26 13:33, Frederic Weisbecker wrote:
> Some workloads with different CPU capacities consume more power with
> timer migration than before. The recently introduced per capacity
> hierarchies were supposed to alleviate this problem. However it appears
> to also regress other types of workloads, especially when plenty of
> capacities live together in the same machine.
> 
> Disable the feature until a reasonable solution is found.
> 
> Fixes: 098cbaad8e57 ("timers/migration: Split per-capacity hierarchies")
> Reported-by: Christian Loehle <christian.loehle@arm.com>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>  kernel/time/timer_migration.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
> index 548d84955f4c..e9d96d96e251 100644
> --- a/kernel/time/timer_migration.c
> +++ b/kernel/time/timer_migration.c
> @@ -1473,7 +1473,7 @@ static unsigned int tmigr_get_capacity(int cpu)
>  	 * timekeeper must then belong to the same hierarchy as all the nohz_full
>  	 * CPUs. Simply turn off capacity awareness when nohz_full is running.
>  	 */
> -	if (tick_nohz_full_enabled())
> +	if (tick_nohz_full_enabled() || !IS_ENABLED(CONFIG_BROKEN))
>  		return SCHED_CAPACITY_SCALE;
>  	else
>  		return arch_scale_cpu_capacity(cpu);

FWIW
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Thanks for looking into this after the late response!

I have something based on avg_idle which doesn't look unreasonable on first glance,
I'll do some more testing and hopefully post it with some number soon!