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Subject[PATCH v6 14/16] sched/core: uclamp: Map TG's clamp values into CPU's clamp buckets
Date
Utilization clamping requires to map each different clamp value into one
of the available clamp buckets used at {en,de}queue time (fast-path).
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
bucket and release the reference to the previous one.

Ensure that, whenever a task group is assigned a specific clamp_value,
this is properly translated into a unique clamp bucket to be used in the
fast-path. Do it by slightly refactoring uclamp_bucket_inc() to make the
(*task_struct) parameter optional and by reusing the code already
available for the per-task API.

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>

---
Changes in v6:
Others:
- wholesale s/group/bucket/
- wholesale s/_{get,put}/_{inc,dec}/ to match refcount APIs
---
include/linux/sched.h | 4 ++--
kernel/sched/core.c | 53 +++++++++++++++++++++++++++++++++----------
2 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 05d286524d70..3f02128fe6b2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -617,8 +617,8 @@ struct sched_dl_entity {
* uclamp_bucket_dec() - for the old clamp value
*
* The active bit is set whenever a task has got an effective clamp bucket
- * and value assigned, which can be different from the user requested ones.
- * This allows to know a task is actually refcounting a CPU's clamp bucket.
+ * and value assigned, and it allows to know a task is actually refcounting a
+ * CPU's clamp bucket.
*/
struct uclamp_se {
unsigned int value : bits_per(SCHED_CAPACITY_SCALE);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ddbd591b305c..734b769db2ca 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1298,9 +1298,9 @@ static void __init init_uclamp(void)
#ifdef CONFIG_UCLAMP_TASK_GROUP
/* Init root TG's clamp bucket */
uc_se = &root_task_group.uclamp[clamp_id];
- uc_se->value = uclamp_none(clamp_id);
- uc_se->bucket_id = 0;
- uc_se->effective.value = uclamp_none(clamp_id);
+ uclamp_bucket_inc(NULL, uc_se, clamp_id, uclamp_none(UCLAMP_MAX));
+ uc_se->effective.bucket_id = uc_se->bucket_id;
+ uc_se->effective.value = uc_se->value;
#endif
}
}
@@ -6880,6 +6880,16 @@ void ia64_set_curr_task(int cpu, struct task_struct *p)
/* task_group_lock serializes the addition/removal of task groups */
static DEFINE_SPINLOCK(task_group_lock);

+static inline void free_uclamp_sched_group(struct task_group *tg)
+{
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+ int clamp_id;
+
+ for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id)
+ uclamp_bucket_dec(clamp_id, tg->uclamp[clamp_id].bucket_id);
+#endif
+}
+
static inline int alloc_uclamp_sched_group(struct task_group *tg,
struct task_group *parent)
{
@@ -6887,12 +6897,12 @@ 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].bucket_id =
- parent->uclamp[clamp_id].bucket_id;
+ uclamp_bucket_inc(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.bucket_id =
+ parent->uclamp[clamp_id].effective.bucket_id;
}
#endif

@@ -6901,6 +6911,7 @@ 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);
@@ -7147,7 +7158,8 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)

#ifdef CONFIG_UCLAMP_TASK_GROUP
static void cpu_util_update_hier(struct cgroup_subsys_state *css,
- int clamp_id, unsigned int value)
+ unsigned int clamp_id, unsigned int bucket_id,
+ unsigned int value)
{
struct cgroup_subsys_state *top_css = css;
struct uclamp_se *uc_se, *uc_parent;
@@ -7159,8 +7171,10 @@ 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;
+ bucket_id = uc_se->effective.bucket_id;
+ }

/*
* Skip the whole subtrees if the current effective clamp is
@@ -7176,12 +7190,15 @@ 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;
+ bucket_id = uc_parent->effective.bucket_id;
+ }
if (uc_se->effective.value == value)
continue;

uc_se->effective.value = value;
+ uc_se->effective.bucket_id = bucket_id;
}
}

@@ -7194,6 +7211,7 @@ 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);
@@ -7204,11 +7222,16 @@ static int cpu_util_min_write_u64(struct cgroup_subsys_state *css,
goto out;
}

+ /* Update TG's reference count */
+ uclamp_bucket_inc(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].bucket_id,
+ min_value);

out:
rcu_read_unlock();
+ mutex_unlock(&uclamp_mutex);

return ret;
}
@@ -7222,6 +7245,7 @@ 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);
@@ -7232,11 +7256,16 @@ static int cpu_util_max_write_u64(struct cgroup_subsys_state *css,
goto out;
}

+ /* Update TG's reference count */
+ uclamp_bucket_inc(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].bucket_id,
+ max_value);

out:
rcu_read_unlock();
+ mutex_unlock(&uclamp_mutex);

return ret;
}
--
2.19.2
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