sched/core: uclamp: update CPU's refcount on clamp changes

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 <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Todd Kjos <tkjos@google.com>
Cc: Joel Fernandes <joelaf@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
---
Changes in v3:
 Message-ID: <CAJuCfpF6=L=0LrmNnJrTNPazT4dWKqNv+thhN0dwpKCgUzs9sg@mail.gmail.com>
 - rename UCLAMP_NONE into UCLAMP_NOT_VALID
 Other:
 - rabased on tip/sched/core

Changes in v2:
 Message-ID: <20180413111900.GF4082@hirez.programming.kicks-ass.net>
 - 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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f058ceb14d25f3bd1edbba14672396a35891b2a7..bc2beedec7bf0ef3e5f309de5099ff1c803410b9 100644 (file)
--- 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 b6d83bfa0eedeff9ca75bc60174c18dd626390b1..a54ed5305f3f458d60303431710fe6a86a7fa65c 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2218,6 +2218,51 @@ 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