Re: [PATCHv2] cpufreq/schedutil: Only bind threads if needed

[Juri Lelli <juri.lelli@redhat.com>]

Hi,

On 27/09/24 09:59, Christian Loehle wrote:
> Remove the unconditional binding of sugov kthreads to the affected CPUs
> if the cpufreq driver indicates that updates can happen from any CPU.
> This allows userspace to set affinities to either save power (waking up
> bigger CPUs on HMP can be expensive) or increasing performance (by
> letting the utilized CPUs run without preemption of the sugov kthread).
> 
> Signed-off-by: Christian Loehle <christian.loehle@arm.com>
> ---
> - v2: Add comment for the dl_task_check_affinity return (Juri)
> v1: https://lore.kernel.org/lkml/480f2140-ea59-4e1d-a68d-18cbcec10941@arm.com/
> 
>  kernel/sched/cpufreq_schedutil.c | 6 +++++-
>  kernel/sched/syscalls.c          | 7 +++++++
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index c6ba15388ea7..10faab849a3e 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -691,7 +691,11 @@ static int sugov_kthread_create(struct sugov_policy *sg_policy)
>  	}
>  
>  	sg_policy->thread = thread;
> -	kthread_bind_mask(thread, policy->related_cpus);
> +	if (policy->dvfs_possible_from_any_cpu)
> +		set_cpus_allowed_ptr(thread, policy->related_cpus);
> +	else
> +		kthread_bind_mask(thread, policy->related_cpus);
> +
>  	init_irq_work(&sg_policy->irq_work, sugov_irq_work);
>  	mutex_init(&sg_policy->work_lock);
>  
> diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
> index aa70beee9895..2ef1cb8626bc 100644
> --- a/kernel/sched/syscalls.c
> +++ b/kernel/sched/syscalls.c
> @@ -1172,6 +1172,13 @@ int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
>  	if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
>  		return 0;
>  
> +	/*
> +	 * The special/sugov task isn't part of regular bandwidth/admission
> +	 * control so let userspace change affinities.
> +	 */
> +	if (dl_entity_is_special(&p->dl))
> +		return 0;
> +
>  	/*
>  	 * Since bandwidth control happens on root_domain basis,
>  	 * if admission test is enabled, we only admit -deadline

For the DEADLINE related bits,

Acked-by: Juri Lelli <juri.lelli@redhat.com>

Thanks,
Juri