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    SubjectRe: [PATCH, v3 2/2] cgroups: introduce timer slack subsystem
    On Wed, Feb 02, 2011 at 02:56:05PM -0800, jacob pan wrote:
    > On Wed, 2 Feb 2011 22:47:36 +0200
    > "Kirill A. Shutsemov" <kirill@shutemov.name> wrote:
    >
    > > From: Kirill A. Shutemov <kirill@shutemov.name>
    > >
    > > 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.
    > >
    > > Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
    > > Idea-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
    > > ---
    > > include/linux/cgroup_subsys.h | 6 +
    > > include/linux/init_task.h | 4 +-
    > > init/Kconfig | 10 ++
    > > kernel/Makefile | 1 +
    > > kernel/cgroup_timer_slack.c | 242
    > > +++++++++++++++++++++++++++++++++++++++++
    >
    > > +
    > > +static int cgroup_timer_slack_check(struct task_struct *task,
    > > + unsigned long slack_ns)
    > > +{
    > > + struct cgroup_subsys_state *css;
    > > + struct timer_slack_cgroup *tslack_cgroup;
    > > +
    >
    > use rcu_read_lock()/unlock?
    > lockdep complains unprotected rcu dereference check.

    Hmm.. I'm not sure, but it looks like lockdep false positive similar to
    cgroup_freezer's (see commit 8b46f88084).
    Paul, am I right?

    > > + css = task_subsys_state(task, timer_slack_subsys.subsys_id);
    > > + tslack_cgroup = container_of(css, struct timer_slack_cgroup,
    > > css); +
    > > + if (slack_ns < tslack_cgroup->min_slack_ns)
    > > + return -EPERM;
    > > + if (slack_ns > tslack_cgroup->max_slack_ns)
    > > + return -EPERM;
    > > + return 0;
    > > +}
    > > +
    >
    > > +
    > > +static struct cftype files[] = {
    > > + {
    > > + .name = "set_slack_ns",
    > > + .write_u64 = tslack_write_set_slack_ns,
    > > + },
    > should we also allow reading of the current slack_ns?

    There is no 'current slack_ns' for a cgroup since any process free to
    change it with prctl().

    > > + {
    > > + .name = "min_slack_ns",
    > > + .private = TIMER_SLACK_MIN,
    > > + .read_u64 = tslack_read_range,
    > > + .write_u64 = tslack_write_range,
    > > + },
    > > + {
    > > + .name = "max_slack_ns",
    > > + .private = TIMER_SLACK_MAX,
    > > + .read_u64 = tslack_read_range,
    > > + .write_u64 = tslack_write_range,
    > > + },
    > > +};
    > > +

    --
    Kirill A. Shutemov


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