Re: [PATCH 1/1] cgroup: make per-cgroup pressure stall tracking configurable

[Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

On Thu, May 13, 2021 at 10:53:49AM -0700, Suren Baghdasaryan wrote:

> +bool cgroup_psi_enabled(void)
> +{
> +	return (cgroup_feature_disable_mask & (1 << OPT_FEATURE_PRESSURE)) == 0;
> +}

> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index cc25a3cff41f..c73efd7d4fba 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -747,9 +747,12 @@ static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
>  #ifdef CONFIG_CGROUPS
>  	struct cgroup *cgroup = NULL;
>  
> -	if (!*iter)
> +	if (!*iter) {
> +		/* Skip to psi_system if per-cgroup accounting is disabled */
> +		if (!cgroup_psi_enabled())
> +			goto update_sys;
>  		cgroup = task->cgroups->dfl_cgrp;
> -	else if (*iter == &psi_system)
> +	} else if (*iter == &psi_system)
>  		return NULL;
>  	else
>  		cgroup = cgroup_parent(*iter);
> @@ -758,6 +761,7 @@ static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
>  		*iter = cgroup;
>  		return cgroup_psi(cgroup);
>  	}
> +update_sys:
>  #else
>  	if (*iter)
>  		return NULL;

I'm confused; shouldn't that do the same as that #else branch? Also, can
you pretty please make cgroup_psi_enabled() a static_key ?