[PATCH RFC 3/8] sched/cpufreq_schedutil: make worker kthread be SCHED_DEADLINE

From: Juri Lelli
Date: Tue May 23 2017 - 04:58:12 EST

Worker kthread needs to be able to change frequency for all other
threads.

Make it special, just under STOP class.

Signed-off-by: Juri Lelli <juri.lelli@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Cc: Luca Abeni <luca.abeni@xxxxxxxxxxxxxxx>
Cc: Claudio Scordino <claudio@xxxxxxxxxxxxxxx>
---
include/linux/sched.h | 1 +
include/uapi/linux/sched.h | 1 +
kernel/sched/core.c | 19 +++++++++++++++++--
kernel/sched/cpufreq_schedutil.c | 15 ++++++++++++---
kernel/sched/deadline.c | 6 ++++++
kernel/sched/sched.h | 8 +++++++-
6 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8127f8bbef56..fd30bec5e199 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1360,6 +1360,7 @@ extern int idle_cpu(int cpu);
extern int sched_setscheduler(struct task_struct *, int, const struct sched_param *);
extern int sched_setscheduler_nocheck(struct task_struct *, int, const struct sched_param *);
extern int sched_setattr(struct task_struct *, const struct sched_attr *);
+extern int sched_setattr_nocheck(struct task_struct *, const struct sched_attr *);
extern struct task_struct *idle_task(int cpu);

/**
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index e2a6c7b3510b..72723859ef74 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -48,5 +48,6 @@
*/
#define SCHED_FLAG_RESET_ON_FORK 0x01
#define SCHED_FLAG_RECLAIM 0x02
+#define SCHED_FLAG_SPECIAL 0x04

#endif /* _UAPI_LINUX_SCHED_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7fc2011c3ce7..ba57e2ef9aef 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2495,6 +2495,9 @@ static int dl_overflow(struct task_struct *p, int policy,
u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0;
int cpus, err = -1;

+ if (attr->sched_flags & SCHED_FLAG_SPECIAL)
+ return 0;
+
/* !deadline task may carry old deadline bandwidth */
if (new_bw == p->dl.dl_bw && task_has_dl_policy(p))
return 0;
@@ -4119,6 +4122,10 @@ __getparam_dl(struct task_struct *p, struct sched_attr *attr)
static bool
__checkparam_dl(const struct sched_attr *attr)
{
+ /* special dl tasks don't actually use any parameter */
+ if (attr->sched_flags & SCHED_FLAG_SPECIAL)
+ return true;
+
/* deadline != 0 */
if (attr->sched_deadline == 0)
return false;
@@ -4205,7 +4212,9 @@ static int __sched_setscheduler(struct task_struct *p,
}

if (attr->sched_flags &
- ~(SCHED_FLAG_RESET_ON_FORK | SCHED_FLAG_RECLAIM))
+ ~(SCHED_FLAG_RESET_ON_FORK |
+ SCHED_FLAG_RECLAIM |
+ SCHED_FLAG_SPECIAL))
return -EINVAL;

/*
@@ -4327,7 +4336,8 @@ static int __sched_setscheduler(struct task_struct *p,
}
#endif
#ifdef CONFIG_SMP
- if (dl_bandwidth_enabled() && dl_policy(policy)) {
+ if (dl_bandwidth_enabled() && dl_policy(policy) &&
+ !(attr->sched_flags & SCHED_FLAG_SPECIAL)) {
cpumask_t *span = rq->rd->span;

/*
@@ -4457,6 +4467,11 @@ int sched_setattr(struct task_struct *p, const struct sched_attr *attr)
}
EXPORT_SYMBOL_GPL(sched_setattr);

+int sched_setattr_nocheck(struct task_struct *p, const struct sched_attr *attr)
+{
+ return __sched_setscheduler(p, attr, false, true);
+}
+
/**
* sched_setscheduler_nocheck - change the scheduling policy and/or RT priority of a thread from kernelspace.
* @p: the task in question.
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 7f1913e265d1..1508109c7f19 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -421,7 +421,16 @@ static void sugov_policy_free(struct sugov_policy *sg_policy)
static int sugov_kthread_create(struct sugov_policy *sg_policy)
{
struct task_struct *thread;
- struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO / 2 };
+ struct sched_attr attr = {
+ .size = sizeof(struct sched_attr),
+ .sched_policy = SCHED_DEADLINE,
+ .sched_flags = SCHED_FLAG_SPECIAL,
+ .sched_nice = 0,
+ .sched_priority = 0,
+ .sched_runtime = 0,
+ .sched_deadline = 0,
+ .sched_period = 0,
+ };
struct cpufreq_policy *policy = sg_policy->policy;
int ret;

@@ -439,10 +448,10 @@ static int sugov_kthread_create(struct sugov_policy *sg_policy)
return PTR_ERR(thread);
}

- ret = sched_setscheduler_nocheck(thread, SCHED_FIFO, &param);
+ ret = sched_setattr_nocheck(thread, &attr);
if (ret) {
kthread_stop(thread);
- pr_warn("%s: failed to set SCHED_FIFO\n", __func__);
+ pr_warn("%s: failed to set SCHED_DEADLINE\n", __func__);
return ret;
}

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fed54b078240..5ee4fd9b1c7f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -187,6 +187,9 @@ static void task_non_contending(struct task_struct *p)
if (dl_se->dl_runtime == 0)
return;

+ if (unlikely(dl_entity_is_special(dl_se)))
+ return;
+
WARN_ON(hrtimer_active(&dl_se->inactive_timer));
WARN_ON(dl_se->dl_non_contending);

@@ -1036,6 +1039,9 @@ static void update_curr_dl(struct rq *rq)

sched_rt_avg_update(rq, delta_exec);

+ if (unlikely(dl_entity_is_special(dl_se)))
+ return;
+
if (unlikely(dl_se->flags & SCHED_FLAG_RECLAIM))
delta_exec = grub_reclaim(delta_exec, rq, &curr->dl);
dl_se->runtime -= delta_exec;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f1e400c6403c..e48cc8762e04 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -155,13 +155,19 @@ static inline int task_has_dl_policy(struct task_struct *p)
return dl_policy(p->policy);
}

+static inline int dl_entity_is_special(struct sched_dl_entity *dl_se)
+{
+ return dl_se->flags & SCHED_FLAG_SPECIAL;
+}
+
/*
* Tells if entity @a should preempt entity @b.
*/
static inline bool
dl_entity_preempt(struct sched_dl_entity *a, struct sched_dl_entity *b)
{
- return dl_time_before(a->deadline, b->deadline);
+ return dl_entity_is_special(a) ||
+ dl_time_before(a->deadline, b->deadline);
}

/*
--
2.11.0