Utilization clamp values enforced on a CPU by a task can be updated at run-time, for example via a sched_setattr syscall, while a task is currently RUNNABLE on that CPU. In these cases, the task can be already refcounting a clamp group for its CPU and thus we need to update this reference to ensure the new constraints are immediately enforced.
Since a clamp value change always implies a clamp group refcount update, this patch hooks into the clamp group refcount getter to trigger a CPU refcount syncup. Such a syncup is required only by currently RUNNABLE tasks which are also referencing at least one valid clamp group. Signed-off-by: Patrick Bellasi <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Paul Turner <[email protected]> Cc: Suren Baghdasaryan <[email protected]> Cc: Todd Kjos <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Juri Lelli <[email protected]> Cc: Dietmar Eggemann <[email protected]> Cc: Morten Rasmussen <[email protected]> Cc: [email protected] Cc: [email protected] --- Changes in v3: Message-ID: <CAJuCfpF6=L=0lrmnnjrtnpazt4dwkqnv+thhn0dwpkcguzs...@mail.gmail.com> - rename UCLAMP_NONE into UCLAMP_NOT_VALID Other: - rabased on tip/sched/core Changes in v2: Message-ID: <[email protected]> - get rid of the group_id back annotation which is not requires at this stage where we have only per-task clamping support. It will be introduce later when CGroups support is added. Other: - rabased on v4.18-rc4 - this code has been split from a previous patch to simplify the review --- kernel/sched/core.c | 61 ++++++++++++++++++++++++++++++++++++++++---- kernel/sched/sched.h | 45 ++++++++++++++++++++++++++++++++ 2 files changed, 101 insertions(+), 5 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f058ceb14d25..bc2beedec7bf 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1065,6 +1065,52 @@ static inline void uclamp_cpu_put(struct rq *rq, struct task_struct *p) uclamp_cpu_put_id(p, rq, clamp_id); } +/** + * uclamp_task_update_active: update the clamp group of a RUNNABLE task + * @p: the task which clamp groups must be updated + * @clamp_id: the clamp index to consider + * @group_id: the clamp group to update + * + * Each time the clamp value of a task group is changed, the old and new clamp + * groups have to be updated for each CPU containing a RUNNABLE task belonging + * to this tasks group. Sleeping tasks are not updated since they will be + * enqueued with the proper clamp group index at their next activation. + */ +static inline void +uclamp_task_update_active(struct task_struct *p, int clamp_id, int group_id) +{ + struct rq_flags rf; + struct rq *rq; + + /* + * Lock the task and the CPU where the task is (or was) queued. + * + * We might lock the (previous) RQ of a !RUNNABLE task, but that's the + * price to pay to safely serialize util_{min,max} updates with + * enqueues, dequeues and migration operations. + * This is the same locking schema used by __set_cpus_allowed_ptr(). + */ + rq = task_rq_lock(p, &rf); + + /* + * The setting of the clamp group is serialized by task_rq_lock(). + * Thus, if the task's task_struct is not referencing a valid group + * index, then that task is not yet RUNNABLE and it's going to be + * enqueued with the proper clamp group value. + */ + if (!uclamp_task_active(p)) + goto done; + + /* Release p's currently referenced clamp group */ + uclamp_cpu_put_id(p, rq, clamp_id); + + /* Get p's new clamp group */ + uclamp_cpu_get_id(p, rq, clamp_id); + +done: + task_rq_unlock(rq, p, &rf); +} + /** * uclamp_group_put: decrease the reference count for a clamp group * @clamp_id: the clamp index which was affected by a task group @@ -1100,6 +1146,7 @@ static inline void uclamp_group_put(int clamp_id, int group_id) /** * 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 * @next_group_id: the clamp group to refcount * @uc_se: the utilization clamp data for the task @@ -1110,9 +1157,10 @@ static inline void uclamp_group_put(int clamp_id, int group_id) * 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. */ -static inline void uclamp_group_get(int clamp_id, int next_group_id, - struct uclamp_se *uc_se, - unsigned int clamp_value) +static inline void uclamp_group_get(struct task_struct *p, + int clamp_id, int next_group_id, + struct uclamp_se *uc_se, + unsigned int clamp_value) { struct uclamp_map *uc_map = &uclamp_maps[clamp_id][0]; int prev_group_id = uc_se->group_id; @@ -1129,6 +1177,9 @@ static inline void uclamp_group_get(int clamp_id, int next_group_id, uc_map[next_group_id].se_count += 1; raw_spin_unlock_irqrestore(&uc_map[next_group_id].se_lock, flags); + /* Update CPU's clamp group refcounts of RUNNABLE task */ + uclamp_task_update_active(p, clamp_id, next_group_id); + /* Release the previous clamp group */ uclamp_group_put(clamp_id, prev_group_id); } @@ -1188,12 +1239,12 @@ static inline int __setscheduler_uclamp(struct task_struct *p, /* Update each required clamp group */ if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { uc_se = &p->uclamp[UCLAMP_MIN]; - uclamp_group_get(UCLAMP_MIN, group_id[UCLAMP_MIN], + uclamp_group_get(p, UCLAMP_MIN, group_id[UCLAMP_MIN], uc_se, attr->sched_util_min); } if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { uc_se = &p->uclamp[UCLAMP_MAX]; - uclamp_group_get(UCLAMP_MAX, group_id[UCLAMP_MAX], + uclamp_group_get(p, UCLAMP_MAX, group_id[UCLAMP_MAX], uc_se, attr->sched_util_max); } diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 8f96926703fc..c9df61d39a03 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2208,6 +2208,51 @@ static inline bool uclamp_group_active(struct uclamp_group *uc_grp, { return uc_grp[group_id].tasks > 0; } + +/** + * uclamp_task_affects: check if a task affects a utilization clamp + * @p: the task to consider + * @clamp_id: the utilization clamp to check + * + * A task affects a clamp index if: + * - it's currently enqueued on a CPU + * - it references a valid clamp group index for the specified clamp index + * + * Return: true if p currently affects the specified clamp_id + */ +static inline bool uclamp_task_affects(struct task_struct *p, int clamp_id) +{ + return (p->uclamp[clamp_id].group_id != UCLAMP_NOT_VALID); +} + +/** + * uclamp_task_active: check if a task is currently clamping a CPU + * @p: the task to check + * + * A task actively affects the utilization clamp of a CPU if: + * - it's currently enqueued or running on that CPU + * - it's refcounted in at least one clamp group of that CPU + * + * Return: true if p is currently clamping the utilization of its CPU. + */ +static inline bool uclamp_task_active(struct task_struct *p) +{ + struct rq *rq = task_rq(p); + int clamp_id; + + lockdep_assert_held(&p->pi_lock); + lockdep_assert_held(&rq->lock); + + if (!task_on_rq_queued(p) && !p->on_cpu) + return false; + + for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) { + if (uclamp_task_affects(p, clamp_id)) + return true; + } + + return false; +} #endif /* CONFIG_UCLAMP_TASK */ #ifdef CONFIG_CPU_FREQ -- 2.18.0
