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    SubjectRe: [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
    Hello,

    Generally looks good to me. Some nitpicks.

    On Fri, Jun 21, 2019 at 09:42:13AM +0100, Patrick Bellasi wrote:
    > @@ -951,6 +951,12 @@ controller implements weight and absolute bandwidth limit models for
    > normal scheduling policy and absolute bandwidth allocation model for
    > realtime scheduling policy.
    >
    > +Cycles distribution is based, by default, on a temporal base and it
    > +does not account for the frequency at which tasks are executed.
    > +The (optional) utilization clamping support allows to enforce a minimum
    > +bandwidth, which should always be provided by a CPU, and a maximum bandwidth,
    > +which should never be exceeded by a CPU.

    I kinda wonder whether the term bandwidth is a bit confusing because
    it's also used for cpu.max/min. Would just calling it frequency be
    clearer?

    > +static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
    > + char *buf, size_t nbytes,
    > + loff_t off)
    > +{
    > + struct task_group *tg;
    > + u64 min_value;
    > + int ret;
    > +
    > + ret = uclamp_scale_from_percent(buf, &min_value);
    > + if (ret)
    > + return ret;
    > + if (min_value > SCHED_CAPACITY_SCALE)
    > + return -ERANGE;
    > +
    > + rcu_read_lock();
    > +
    > + tg = css_tg(of_css(of));
    > + if (tg == &root_task_group) {
    > + ret = -EINVAL;
    > + goto out;
    > + }

    I don't think you need the above check.

    > + if (tg->uclamp_req[UCLAMP_MIN].value == min_value)
    > + goto out;
    > + if (tg->uclamp_req[UCLAMP_MAX].value < min_value) {
    > + ret = -EINVAL;

    So, uclamp.max limits the maximum freq% can get and uclamp.min limits
    hte maximum freq% protection can get in the subtree. Let's say
    uclamp.max is 50% and uclamp.min is 100%. It means that protection is
    not limited but the actual freq% is limited upto 50%, which isn't
    necessarily invalid. For a simple example, a user might be saying
    that they want to get whatever protection they can get from its parent
    but wanna limit eventual freq at 50% and it isn't too difficult to
    imagine cases where the two knobs are configured separately especially
    configuration is being managed hierarchically / automatically.

    tl;dr is that we don't need the above restriction and shouldn't
    generally be restricting configurations when they don't need to.

    Thanks.

    --
    tejun

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