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SubjectRe: [PATCH v2 11/12] sched/core: uclamp: update CPU's refcount on TG's clamp changes
On Mon, Jul 16, 2018 at 1:29 AM, Patrick Bellasi
<patrick.bellasi@arm.com> wrote:
> When a task group refcounts a new clamp group, we need to ensure that
> the new clamp values are immediately enforced to all its tasks which are
> currently RUNNABLE. This is to ensure that all currently RUNNABLE task

tasks

> are boosted and/or clamped as requested as soon as possible.
>
> Let's ensure that, whenever a new clamp group is refcounted by a task
> group, all its RUNNABLE tasks are correctly accounted in their
> respective CPUs. We do that by slightly refactoring uclamp_group_get()
> to get an additional parameter *cgroup_subsys_state which, when
> provided, it's used to walk the list of tasks in the correspond TGs and

corresponding TGs

> update the RUNNABLE ones.
>
> This is a "brute force" solution which allows to reuse the same refcount
> update code already used by the per-task API. That's also the only way
> to ensure a prompt enforcement of new clamp constraints on RUNNABLE
> tasks, as soon as a task group attribute is tweaked.
>
> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Paul Turner <pjt@google.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Steve Muckle <smuckle@google.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Morten Rasmussen <morten.rasmussen@arm.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> ---
> kernel/sched/core.c | 42 ++++++++++++++++++++++++++++++++++--------
> 1 file changed, 34 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 50613d3d5b83..42cff5ffddae 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1198,21 +1198,43 @@ static inline void uclamp_group_put(int clamp_id, int group_id)
> raw_spin_unlock_irqrestore(&uc_map[group_id].se_lock, flags);
> }
>
> +static inline void uclamp_group_get_tg(struct cgroup_subsys_state *css,
> + int clamp_id, unsigned int group_id)
> +{
> + struct css_task_iter it;
> + struct task_struct *p;
> +
> + /* Update clamp groups for RUNNABLE tasks in this TG */
> + css_task_iter_start(css, 0, &it);
> + while ((p = css_task_iter_next(&it)))
> + uclamp_task_update_active(p, clamp_id, group_id);
> + css_task_iter_end(&it);
> +}
> +
> /**
> * uclamp_group_get: increase the reference count for a clamp group
> * @p: the task which clamp value must be tracked
> - * @clamp_id: the clamp index affected by the task
> - * @uc_se: the utilization clamp data for the task
> - * @clamp_value: the new clamp value for the task
> + * @css: the task group which clamp value must be tracked
> + * @clamp_id: the clamp index affected by the task (group)
> + * @uc_se: the utilization clamp data for the task (group)
> + * @clamp_value: the new clamp value for the task (group)
> *
> * Each time a task changes its utilization clamp value, for a specified clamp
> * index, we need to find an available clamp group which can be used to track
> * this new clamp value. The corresponding clamp group index will be used by
> * the task to reference count the clamp value on CPUs while enqueued.
> *
> + * When the cgroup's cpu controller utilization clamping support is enabled,
> + * each task group has a set of clamp values which are used to restrict the
> + * corresponding task specific clamp values.
> + * When a clamp value for a task group is changed, all the (active) tasks
> + * belonging to that task group must be update to ensure they are refcounting

must be updated

> + * the correct CPU's clamp value.
> + *
> * Return: -ENOSPC if there are no available clamp groups, 0 on success.
> */
> static inline int uclamp_group_get(struct task_struct *p,
> + struct cgroup_subsys_state *css,
> int clamp_id, struct uclamp_se *uc_se,
> unsigned int clamp_value)
> {
> @@ -1240,6 +1262,10 @@ static inline int uclamp_group_get(struct task_struct *p,
> uc_map[next_group_id].se_count += 1;
> raw_spin_unlock_irqrestore(&uc_map[next_group_id].se_lock, flags);
>
> + /* Newly created TG don't have tasks assigned */
> + if (css)
> + uclamp_group_get_tg(css, clamp_id, next_group_id);
> +
> /* Update CPU's clamp group refcounts of RUNNABLE task */
> if (p)
> uclamp_task_update_active(p, clamp_id, next_group_id);
> @@ -1307,7 +1333,7 @@ static inline int alloc_uclamp_sched_group(struct task_group *tg,
> uc_se->value = parent->uclamp[clamp_id].value;
> uc_se->group_id = UCLAMP_NONE;
>
> - if (uclamp_group_get(NULL, clamp_id, uc_se,
> + if (uclamp_group_get(NULL, NULL, clamp_id, uc_se,
> parent->uclamp[clamp_id].value)) {
> ret = 0;
> goto out;
> @@ -1362,12 +1388,12 @@ static inline int __setscheduler_uclamp(struct task_struct *p,
>
> /* Update min utilization clamp */
> uc_se = &p->uclamp[UCLAMP_MIN];
> - retval |= uclamp_group_get(p, UCLAMP_MIN, uc_se,
> + retval |= uclamp_group_get(p, NULL, UCLAMP_MIN, uc_se,
> attr->sched_util_min);
>
> /* Update max utilization clamp */
> uc_se = &p->uclamp[UCLAMP_MAX];
> - retval |= uclamp_group_get(p, UCLAMP_MAX, uc_se,
> + retval |= uclamp_group_get(p, NULL, UCLAMP_MAX, uc_se,
> attr->sched_util_max);
>
> mutex_unlock(&uclamp_mutex);
> @@ -7274,7 +7300,7 @@ static int cpu_util_min_write_u64(struct cgroup_subsys_state *css,
>
> /* Update TG's reference count */
> uc_se = &tg->uclamp[UCLAMP_MIN];
> - ret = uclamp_group_get(NULL, UCLAMP_MIN, uc_se, min_value);
> + ret = uclamp_group_get(NULL, css, UCLAMP_MIN, uc_se, min_value);
>
> out:
> rcu_read_unlock();
> @@ -7306,7 +7332,7 @@ static int cpu_util_max_write_u64(struct cgroup_subsys_state *css,
>
> /* Update TG's reference count */
> uc_se = &tg->uclamp[UCLAMP_MAX];
> - ret = uclamp_group_get(NULL, UCLAMP_MAX, uc_se, max_value);
> + ret = uclamp_group_get(NULL, css, UCLAMP_MAX, uc_se, max_value);
>
> out:
> rcu_read_unlock();
> --
> 2.17.1
>

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