linux-kernel - Re: [PATCH 2/2] sched/psi: iterate through cgroups directly

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Date:   Wed, 8 Feb 2023 18:29:56 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Kairui Song <kasong@...cent.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Chengming Zhou <zhouchengming@...edance.com>,
        Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kairui Song <ryncsn@...il.com>
Subject: Re: [PATCH 2/2] sched/psi: iterate through cgroups directly

On Thu, Feb 09, 2023 at 12:16:54AM +0800, Kairui Song <ryncsn@...il.com> wrote:
> Signed-off-by: Kairui Song <kasong@...cent.com>
> Signed-off-by: Kairui Song <ryncsn@...il.com>

Typo?

> -static inline struct psi_group *task_psi_group(struct task_struct *task)
> +static inline struct psi_group *psi_iter_first(struct task_struct *task, void **iter)
>  {
>  #ifdef CONFIG_CGROUPS
> -	if (static_branch_likely(&psi_cgroups_enabled))
> -		return cgroup_psi(task_dfl_cgroup(task));
> +	if (static_branch_likely(&psi_cgroups_enabled)) {
> +		struct cgroup *cgroup = task_dfl_cgroup(task);
> +
> +		*iter = cgroup_parent(cgroup);

This seems to skip a cgroup level -- maybe that's the observed
performance gain?

> +		return cgroup_psi(cgroup);
> +	}
>  #endif
>  	return &psi_system;
>  }

Michal

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