Re: [RFC PATCH 3/5] sched/fair: Update overloaded mask in presence of pushable task

[Aaron Lu <ziqianlu@bytedance.com>]

Hi Prateek,

On Wed, Apr 09, 2025 at 11:15:37AM +0000, K Prateek Nayak wrote:
> In presence of pushable tasks on the CPU, set it on the newly introduced
> "overloaded+mask" in sched_domain_shared struct. This will be used by
> the newidle balance to limit the scanning to these overloaded CPUs since
> they contain tasks that could be run on the newly idle target.
> 
> Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
> ---
>  kernel/sched/fair.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 98d3ed2078cd..834fcdd15cac 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8559,6 +8559,24 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
>  	return target;
>  }
>  
> +static inline void update_overloaded_mask(int cpu, bool contains_pushable)
> +{
> +	struct sched_domain_shared *sd_share = rcu_dereference(per_cpu(sd_llc_shared, cpu));

I got a suspicious RCU usage warning for this line while testing your
series. Since rq lock is held here, rcu_dereference() should not be
necessary.

> +	cpumask_var_t overloaded_mask;
> +
> +	if (!sd_share)
> +		return;
> +
> +	overloaded_mask = sd_share->overloaded_mask;
> +	if (!overloaded_mask)
> +		return;
> +
> +	if (contains_pushable)
> +		cpumask_set_cpu(cpu, overloaded_mask);
> +	else
> +		cpumask_clear_cpu(cpu, overloaded_mask);
> +}