Re: [RFC v3 1/5] sched/core: add capacity constraints to CPU controller

Joel Fernandes (Google)
2017-03-13T10:46:13Z

On Tue, Feb 28, 2017 at 6:38 AM, Patrick Bellasi
<patrick.bellasi@arm.com> wrote:
> The CPU CGroup controller allows to assign a specified (maximum)
> bandwidth to tasks within a group, however it does not enforce any
> constraint on how such bandwidth can be consumed.
> With the integration of schedutil, the scheduler has now the proper
> information about a task to select the most suitable frequency to
> satisfy tasks needs.
[..]

> +static u64 cpu_capacity_min_read_u64(struct cgroup_subsys_state *css,
> + struct cftype *cft)
> +{
> + struct task_group *tg;
> + u64 min_capacity;
> +
> + rcu_read_lock();
> + tg = css_tg(css);
> + min_capacity = tg->cap_clamp[CAP_CLAMP_MIN];

Shouldn't the cap_clamp be accessed with READ_ONCE (and WRITE_ONCE in
the write path) to avoid load-tearing?

Thanks,
Joel