From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paul Menage <menage-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH, v3 2/2] cgroups: introduce timer slack subsystem
Date: Wed, 2 Feb 2011 15:23:15 -0800
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On Wed, Feb 2, 2011 at 12:47 PM, Kirill A. Shutsemov
<kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org> wrote:
> From: Kirill A. Shutemov <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>
>
> Provides a way of tasks grouping by timer slack value. Introduces per
> cgroup max and min timer slack value. When a task attaches to a cgroup,
> its timer slack value adjusts (if needed) to fit min-max range.
>
> It also provides a way to set timer slack value for all tasks in the
> cgroup at once.
>
> This functionality is useful in mobile devices where certain background
> apps are attached to a cgroup and minimum wakeups are desired.

If you really want to be able to make this modular, I'd be inclined to
make the check_timer_slack hook just default to NULL, rather than
introducing dummy_timer_slack_check()


> +
> +static int tslack_write_range(struct cgroup *cgroup, struct cftype *cft,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 u64 val)
> +{
> + =A0 =A0 =A0 struct timer_slack_cgroup *tslack_cgroup;
> + =A0 =A0 =A0 struct cgroup_iter it;
> + =A0 =A0 =A0 struct task_struct *task;
> +
> + =A0 =A0 =A0 if (!val)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -EINVAL;
> +
> + =A0 =A0 =A0 tslack_cgroup =3D cgroup_to_tslack_cgroup(cgroup);
> + =A0 =A0 =A0 switch (cft->private) {
> + =A0 =A0 =A0 case TIMER_SLACK_MIN:
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (val > tslack_cgroup->max_slack_ns)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -EINVAL;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 tslack_cgroup->min_slack_ns =3D val;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 break;
> + =A0 =A0 =A0 case TIMER_SLACK_MAX:
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (val < tslack_cgroup->min_slack_ns)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -EINVAL;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 tslack_cgroup->max_slack_ns =3D val;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 break;
> + =A0 =A0 =A0 default:
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 BUG();
> + =A0 =A0 =A0 }
> +

Don't we want to keep the min/max applied hierarchically as well? i.e.
a child can't set its min/max outside the range of its parents?

> +
> +static int __init init_cgroup_timer_slack(void)
> +{
> + =A0 =A0 =A0 BUG_ON(timer_slack_check !=3D dummy_timer_slack_check);

Better to make this just fail the initialization if someone else has
already claimed the hook, rather than crashing.

Paul