Utilization clamping requires to map each different clamp value into one
of the available clamp groups used in the scheduler fast-path to account
for RUNNABLE tasks. Thus, each time a TG's clamp value sysfs attribute
is updated via:
cpu_util_{min,max}_write_u64()
we need to update the task group reference to the new value's clamp
group and release the reference to the previous one.
Let's ensure that, whenever a task group is assigned a specific
clamp_value, this is properly translated into a unique clamp group to be
used in the fast-path (i.e. at enqueue/dequeue time).
We do that by slightly refactoring uclamp_group_get() to make the
*task_struct parameter optional. This allows to re-use the code already
available for the support of the per-task API.
Signed-off-by: Patrick Bellasi <patrick.bell...@arm.com>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Tejun Heo <t...@kernel.org>
Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
Cc: Viresh Kumar <viresh.ku...@linaro.org>
Cc: Suren Baghdasaryan <sur...@google.com>
Cc: Todd Kjos <tk...@google.com>
Cc: Joel Fernandes <joe...@google.com>
Cc: Juri Lelli <juri.le...@redhat.com>
Cc: Quentin Perret <quentin.per...@arm.com>
Cc: Dietmar Eggemann <dietmar.eggem...@arm.com>
Cc: Morten Rasmussen <morten.rasmus...@arm.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux...@vger.kernel.org
---
Changes in v5:
Others:
- rebased on v4.19
Changes in v4:
Others:
- rebased on v4.19-rc1
Changes in v3:
Message-ID:
<CAJuCfpF6=L=0lrmnnjrtnpazt4dwkqnv+thhn0dwpkcguzs...@mail.gmail.com>
- add explicit calls to uclamp_group_find(), which is now not more
part of uclamp_group_get()
Others:
- rebased on tip/sched/core
Changes in v2:
- rebased on v4.18-rc4
- this code has been split from a previous patch to simplify the review
---
include/linux/sched.h | 7 +++--
kernel/sched/core.c | 64 +++++++++++++++++++++++++++++++++++--------
2 files changed, 56 insertions(+), 15 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d3f6bf62ab3f..7698e7554892 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -601,9 +601,10 @@ struct sched_dl_entity {
* clamp group index (group_id), i.e.
* index of the per-cpu RUNNABLE tasks refcounting array
*
- * The mapped bit is set whenever a task has been mapped on a clamp group for
- * the first time. When this bit is set, any clamp group get (for a new clamp
- * value) will be matches by a clamp group put (for the old clamp value).
+ * The mapped bit is set whenever a scheduling entity has been mapped on a
+ * clamp group for the first time. When this bit is set, any clamp group get
+ * (for a new clamp value) will be matches by a clamp group put (for the old
+ * clamp value).
*
* The active bit is set whenever a task has got an effective clamp group
* and value assigned, which can be different from the user requested ones.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cb49bffb3da8..3dcd1c17a244 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1396,9 +1396,9 @@ static void __init init_uclamp(void)
#ifdef CONFIG_UCLAMP_TASK_GROUP
/* Init root TG's clamp group */
uc_se = &root_task_group.uclamp[clamp_id];
- uc_se->value = uclamp_none(clamp_id);
- uc_se->group_id = 0;
- uc_se->effective.value = uclamp_none(clamp_id);
+ uclamp_group_get(NULL, uc_se, clamp_id,
uclamp_none(UCLAMP_MAX));
+ uc_se->effective.group_id = uc_se->group_id;
+ uc_se->effective.value = uc_se->value;
#endif
}
}
@@ -6971,6 +6971,22 @@ void ia64_set_curr_task(int cpu, struct task_struct *p)
static DEFINE_SPINLOCK(task_group_lock);
#ifdef CONFIG_UCLAMP_TASK_GROUP
+/*
+ * free_uclamp_sched_group: release utilization clamp references of a TG
+ * @tg: the task group being removed
+ *
+ * An empty task group can be removed only when it has no more tasks or child
+ * groups. This means that we can also safely release all the reference
+ * counting to clamp groups.
+ */
+static inline void free_uclamp_sched_group(struct task_group *tg)
+{
+ int clamp_id;
+
+ for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id)
+ uclamp_group_put(clamp_id, tg->uclamp[clamp_id].group_id);
+}
+
/**
* alloc_uclamp_sched_group: initialize a new TG's for utilization clamping
* @tg: the newly created task group
@@ -6989,17 +7005,18 @@ static inline int alloc_uclamp_sched_group(struct
task_group *tg,
int clamp_id;
for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
- tg->uclamp[clamp_id].value =
- parent->uclamp[clamp_id].value;
- tg->uclamp[clamp_id].group_id =
- parent->uclamp[clamp_id].group_id;
+ uclamp_group_get(NULL, &tg->uclamp[clamp_id], clamp_id,
+ parent->uclamp[clamp_id].value);
tg->uclamp[clamp_id].effective.value =
parent->uclamp[clamp_id].effective.value;
+ tg->uclamp[clamp_id].effective.group_id =
+ parent->uclamp[clamp_id].effective.group_id;
}
return 1;
}
#else
+static inline void free_uclamp_sched_group(struct task_group *tg) { }
static inline int alloc_uclamp_sched_group(struct task_group *tg,
struct task_group *parent)
{
@@ -7009,6 +7026,7 @@ static inline int alloc_uclamp_sched_group(struct
task_group *tg,
static void sched_free_group(struct task_group *tg)
{
+ free_uclamp_sched_group(tg);
free_fair_sched_group(tg);
free_rt_sched_group(tg);
autogroup_free(tg);
@@ -7258,6 +7276,7 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
* cpu_util_update_hier: propagate effective clamp down the hierarchy
* @css: the task group to update
* @clamp_id: the clamp index to update
+ * @group_id: the group index mapping the new task clamp value
* @value: the new task group clamp value
*
* The effective clamp for a TG is expected to track the most restrictive
@@ -7277,9 +7296,13 @@ static void cpu_cgroup_attach(struct cgroup_taskset
*tset)
* be propagated down to all the descendants. When a subgroup is found which
* has already its effective clamp value matching its clamp value, then we can
* safely skip all its descendants which are granted to be already in sync.
+ *
+ * The TG's group_id is also updated to ensure it tracks the effective clamp
+ * value.
*/
static void cpu_util_update_hier(struct cgroup_subsys_state *css,
- int clamp_id, unsigned int value)
+ unsigned int clamp_id, unsigned int group_id,
+ unsigned int value)
{
struct cgroup_subsys_state *top_css = css;
struct uclamp_se *uc_se, *uc_parent;
@@ -7291,8 +7314,10 @@ static void cpu_util_update_hier(struct
cgroup_subsys_state *css,
* groups we consider their current value.
*/
uc_se = &css_tg(css)->uclamp[clamp_id];
- if (css != top_css)
+ if (css != top_css) {
value = uc_se->value;
+ group_id = uc_se->effective.group_id;
+ }
/*
* Skip the whole subtrees if the current effective clamp is
@@ -7308,12 +7333,15 @@ static void cpu_util_update_hier(struct
cgroup_subsys_state *css,
}
/* Propagate the most restrictive effective value */
- if (uc_parent->effective.value < value)
+ if (uc_parent->effective.value < value) {
value = uc_parent->effective.value;
+ group_id = uc_parent->effective.group_id;
+ }
if (uc_se->effective.value == value)
continue;
uc_se->effective.value = value;
+ uc_se->effective.group_id = group_id;
}
}
@@ -7326,6 +7354,7 @@ static int cpu_util_min_write_u64(struct
cgroup_subsys_state *css,
if (min_value > SCHED_CAPACITY_SCALE)
return -ERANGE;
+ mutex_lock(&uclamp_mutex);
rcu_read_lock();
tg = css_tg(css);
@@ -7336,11 +7365,16 @@ static int cpu_util_min_write_u64(struct
cgroup_subsys_state *css,
goto out;
}
+ /* Update TG's reference count */
+ uclamp_group_get(NULL, &tg->uclamp[UCLAMP_MIN], UCLAMP_MIN, min_value);
+
/* Update effective clamps to track the most restrictive value */
- cpu_util_update_hier(css, UCLAMP_MIN, min_value);
+ cpu_util_update_hier(css, UCLAMP_MIN, tg->uclamp[UCLAMP_MIN].group_id,
+ min_value);
out:
rcu_read_unlock();
+ mutex_unlock(&uclamp_mutex);
return ret;
}
@@ -7354,6 +7388,7 @@ static int cpu_util_max_write_u64(struct
cgroup_subsys_state *css,
if (max_value > SCHED_CAPACITY_SCALE)
return -ERANGE;
+ mutex_lock(&uclamp_mutex);
rcu_read_lock();
tg = css_tg(css);
@@ -7364,11 +7399,16 @@ static int cpu_util_max_write_u64(struct
cgroup_subsys_state *css,
goto out;
}
+ /* Update TG's reference count */
+ uclamp_group_get(NULL, &tg->uclamp[UCLAMP_MAX], UCLAMP_MAX, max_value);
+
/* Update effective clamps to track the most restrictive value */
- cpu_util_update_hier(css, UCLAMP_MAX, max_value);
+ cpu_util_update_hier(css, UCLAMP_MAX, tg->uclamp[UCLAMP_MAX].group_id,
+ max_value);
out:
rcu_read_unlock();
+ mutex_unlock(&uclamp_mutex);
return ret;
}
--
2.18.0
