[PATCH v2 0/2] sched: Return NULL when entity isn't a task

[PATCH v2 0/2] sched: Return NULL when entity isn't a task

[Yajun Deng]

If the entity isn't a task, return the task struct is meaningless.
Return NULL when entity isn't a task that makes the code more concise.

v1 -> v2: 
fix 'struct rt_rq' no member named 'highest_prio'.

Yajun Deng (2):
  sched/fair: Return NULL when entity isn't a task in task_of()
  sched/rt: Return NULL when rt entity isn't a task in rt_task_of()

 kernel/sched/fair.c  | 50 ++++++++++++++++++------------------
 kernel/sched/rt.c    | 60 +++++++++++++-------------------------------
 kernel/sched/sched.h |  4 ++-
 3 files changed, 44 insertions(+), 70 deletions(-)

-- 
2.25.1

[PATCH v2 1/2] sched/fair: Return NULL when entity isn't a task in task_of()

[Yajun Deng]

Before calling task_of(), we need to make sure that the entity is a task.
There is also a warning in task_of() if the entity isn't a task. That
means we need to check the entity twice. If the entity isn't a task,
return the task struct is meaningless.

Return NULL when entity isn't a task in task_of(), and call task_of()
instead of entity_is_task() when we need a task_struct.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
 kernel/sched/fair.c  | 50 +++++++++++++++++++++-----------------------
 kernel/sched/sched.h |  4 +++-
 2 files changed, 27 insertions(+), 27 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bcd0f230e21f..5003c8501398 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -470,8 +470,10 @@ static int cfs_rq_is_idle(struct cfs_rq *cfs_rq)
 
 static int se_is_idle(struct sched_entity *se)
 {
-	if (entity_is_task(se))
-		return task_has_idle_policy(task_of(se));
+	struct task_struct *p = task_of(se);
+
+	if (p)
+		return task_has_idle_policy(p);
 	return cfs_rq_is_idle(group_cfs_rq(se));
 }
 
@@ -1156,6 +1158,7 @@ s64 update_curr_common(struct rq *rq)
 static void update_curr(struct cfs_rq *cfs_rq)
 {
 	struct sched_entity *curr = cfs_rq->curr;
+	struct task_struct *p;
 	s64 delta_exec;
 
 	if (unlikely(!curr))
@@ -1169,8 +1172,9 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	update_deadline(cfs_rq, curr);
 	update_min_vruntime(cfs_rq);
 
-	if (entity_is_task(curr))
-		update_curr_task(task_of(curr), delta_exec);
+	p = task_of(curr);
+	if (p)
+		update_curr_task(p, delta_exec);
 
 	account_cfs_rq_runtime(cfs_rq, delta_exec);
 }
@@ -1184,24 +1188,19 @@ static inline void
 update_stats_wait_start_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	struct sched_statistics *stats;
-	struct task_struct *p = NULL;
 
 	if (!schedstat_enabled())
 		return;
 
 	stats = __schedstats_from_se(se);
 
-	if (entity_is_task(se))
-		p = task_of(se);
-
-	__update_stats_wait_start(rq_of(cfs_rq), p, stats);
+	__update_stats_wait_start(rq_of(cfs_rq), task_of(se), stats);
 }
 
 static inline void
 update_stats_wait_end_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	struct sched_statistics *stats;
-	struct task_struct *p = NULL;
 
 	if (!schedstat_enabled())
 		return;
@@ -1217,27 +1216,20 @@ update_stats_wait_end_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	if (unlikely(!schedstat_val(stats->wait_start)))
 		return;
 
-	if (entity_is_task(se))
-		p = task_of(se);
-
-	__update_stats_wait_end(rq_of(cfs_rq), p, stats);
+	__update_stats_wait_end(rq_of(cfs_rq), task_of(se), stats);
 }
 
 static inline void
 update_stats_enqueue_sleeper_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	struct sched_statistics *stats;
-	struct task_struct *tsk = NULL;
 
 	if (!schedstat_enabled())
 		return;
 
 	stats = __schedstats_from_se(se);
 
-	if (entity_is_task(se))
-		tsk = task_of(se);
-
-	__update_stats_enqueue_sleeper(rq_of(cfs_rq), tsk, stats);
+	__update_stats_enqueue_sleeper(rq_of(cfs_rq), task_of(se), stats);
 }
 
 /*
@@ -1263,6 +1255,7 @@ update_stats_enqueue_fair(struct cfs_rq *cfs_rq, struct sched_entity *se, int fl
 static inline void
 update_stats_dequeue_fair(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
+	struct task_struct *tsk;
 
 	if (!schedstat_enabled())
 		return;
@@ -1274,8 +1267,8 @@ update_stats_dequeue_fair(struct cfs_rq *cfs_rq, struct sched_entity *se, int fl
 	if (se != cfs_rq->curr)
 		update_stats_wait_end_fair(cfs_rq, se);
 
-	if ((flags & DEQUEUE_SLEEP) && entity_is_task(se)) {
-		struct task_struct *tsk = task_of(se);
+	tsk = task_of(se);
+	if ((flags & DEQUEUE_SLEEP) && tsk) {
 		unsigned int state;
 
 		/* XXX racy against TTWU */
@@ -3569,12 +3562,14 @@ static inline void update_scan_period(struct task_struct *p, int new_cpu)
 static void
 account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	struct task_struct *p = task_of(se);
+
 	update_load_add(&cfs_rq->load, se->load.weight);
 #ifdef CONFIG_SMP
-	if (entity_is_task(se)) {
+	if (p) {
 		struct rq *rq = rq_of(cfs_rq);
 
-		account_numa_enqueue(rq, task_of(se));
+		account_numa_enqueue(rq, p);
 		list_add(&se->group_node, &rq->cfs_tasks);
 	}
 #endif
@@ -3586,10 +3581,12 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static void
 account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	struct task_struct *p = task_of(se);
+
 	update_load_sub(&cfs_rq->load, se->load.weight);
 #ifdef CONFIG_SMP
-	if (entity_is_task(se)) {
-		account_numa_dequeue(rq_of(cfs_rq), task_of(se));
+	if (p) {
+		account_numa_dequeue(rq_of(cfs_rq), p);
 		list_del_init(&se->group_node);
 	}
 #endif
@@ -5323,9 +5320,10 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
 static void
 dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
+	struct task_struct *p = task_of(se);
 	int action = UPDATE_TG;
 
-	if (entity_is_task(se) && task_on_rq_migrating(task_of(se)))
+	if (p && task_on_rq_migrating(p))
 		action |= DO_DETACH;
 
 	/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 001fe047bd5d..6baba9ebcde1 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1432,7 +1432,9 @@ static inline void update_idle_core(struct rq *rq) { }
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static inline struct task_struct *task_of(struct sched_entity *se)
 {
-	SCHED_WARN_ON(!entity_is_task(se));
+	if (!entity_is_task(se))
+		return NULL;
+
 	return container_of(se, struct task_struct, se);
 }
 
-- 
2.25.1

[PATCH v2 2/2] sched/rt: Return NULL when rt entity isn't a task in rt_task_of()

[Yajun Deng]

Before calling rt_task_of(), we need to make sure that the rt entity is
a task. There is also a warning in rt_task_of() if the rt entity isn't a
task. That means we need to check the rt entity twice. If the rt entity
isn't a task, return the task struct is meaningless.

Return NULL when rt entity isn't a task in rt_task_of(), and call
rt_task_of() instead of rt_entity_is_task() when we need a task_struct.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
v2: fix 'struct rt_rq' no member named 'highest_prio'.
v1: https://lore.kernel.org/all/20231201022704.3526377-1-yajun.deng@linux.dev/
---
 kernel/sched/rt.c | 60 ++++++++++++++---------------------------------
 1 file changed, 17 insertions(+), 43 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 40d24f64b444..061f5f005c35 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -169,9 +169,9 @@ static void destroy_rt_bandwidth(struct rt_bandwidth *rt_b)
 
 static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
 {
-#ifdef CONFIG_SCHED_DEBUG
-	WARN_ON_ONCE(!rt_entity_is_task(rt_se));
-#endif
+	if (!rt_entity_is_task(rt_se))
+		return NULL;
+
 	return container_of(rt_se, struct task_struct, rt);
 }
 
@@ -1266,54 +1266,34 @@ static void __delist_rt_entity(struct sched_rt_entity *rt_se, struct rt_prio_arr
 	rt_se->on_list = 0;
 }
 
-static inline struct sched_statistics *
-__schedstats_from_rt_se(struct sched_rt_entity *rt_se)
-{
-#ifdef CONFIG_RT_GROUP_SCHED
-	/* schedstats is not supported for rt group. */
-	if (!rt_entity_is_task(rt_se))
-		return NULL;
-#endif
-
-	return &rt_task_of(rt_se)->stats;
-}
-
 static inline void
 update_stats_wait_start_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
 {
-	struct sched_statistics *stats;
-	struct task_struct *p = NULL;
+	struct task_struct *p;
 
 	if (!schedstat_enabled())
 		return;
 
-	if (rt_entity_is_task(rt_se))
-		p = rt_task_of(rt_se);
-
-	stats = __schedstats_from_rt_se(rt_se);
-	if (!stats)
+	p = rt_task_of(rt_se);
+	if (!p)
 		return;
 
-	__update_stats_wait_start(rq_of_rt_rq(rt_rq), p, stats);
+	__update_stats_wait_start(rq_of_rt_rq(rt_rq), p, &p->stats);
 }
 
 static inline void
 update_stats_enqueue_sleeper_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
 {
-	struct sched_statistics *stats;
-	struct task_struct *p = NULL;
+	struct task_struct *p;
 
 	if (!schedstat_enabled())
 		return;
 
-	if (rt_entity_is_task(rt_se))
-		p = rt_task_of(rt_se);
-
-	stats = __schedstats_from_rt_se(rt_se);
-	if (!stats)
+	p = rt_task_of(rt_se);
+	if (!p)
 		return;
 
-	__update_stats_enqueue_sleeper(rq_of_rt_rq(rt_rq), p, stats);
+	__update_stats_enqueue_sleeper(rq_of_rt_rq(rt_rq), p, &p->stats);
 }
 
 static inline void
@@ -1330,34 +1310,28 @@ update_stats_enqueue_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se,
 static inline void
 update_stats_wait_end_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
 {
-	struct sched_statistics *stats;
-	struct task_struct *p = NULL;
+	struct task_struct *p;
 
 	if (!schedstat_enabled())
 		return;
 
-	if (rt_entity_is_task(rt_se))
-		p = rt_task_of(rt_se);
-
-	stats = __schedstats_from_rt_se(rt_se);
-	if (!stats)
+	p = rt_task_of(rt_se);
+	if (!p)
 		return;
 
-	__update_stats_wait_end(rq_of_rt_rq(rt_rq), p, stats);
+	__update_stats_wait_end(rq_of_rt_rq(rt_rq), p, &p->stats);
 }
 
 static inline void
 update_stats_dequeue_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se,
 			int flags)
 {
-	struct task_struct *p = NULL;
+	struct task_struct *p;
 
 	if (!schedstat_enabled())
 		return;
 
-	if (rt_entity_is_task(rt_se))
-		p = rt_task_of(rt_se);
-
+	p = rt_task_of(rt_se);
 	if ((flags & DEQUEUE_SLEEP) && p) {
 		unsigned int state;
 
-- 
2.25.1

Re: [PATCH v2 0/2] sched: Return NULL when entity isn't a task

[Yajun Deng]

Kindly ping...

Thanks


On 2023/12/6 14:33, Yajun Deng wrote:
> If the entity isn't a task, return the task struct is meaningless.
> Return NULL when entity isn't a task that makes the code more concise.
>
> v1 -> v2:
> fix 'struct rt_rq' no member named 'highest_prio'.
>
> Yajun Deng (2):
>    sched/fair: Return NULL when entity isn't a task in task_of()
>    sched/rt: Return NULL when rt entity isn't a task in rt_task_of()
>
>   kernel/sched/fair.c  | 50 ++++++++++++++++++------------------
>   kernel/sched/rt.c    | 60 +++++++++++++-------------------------------
>   kernel/sched/sched.h |  4 ++-
>   3 files changed, 44 insertions(+), 70 deletions(-)
>

Re: [PATCH v2 1/2] sched/fair: Return NULL when entity isn't a task in task_of()

[Steven Rostedt]

On Wed,  6 Dec 2023 14:33:59 +0800
Yajun Deng <yajun.deng@linux.dev> wrote:

> Before calling task_of(), we need to make sure that the entity is a task.
> There is also a warning in task_of() if the entity isn't a task. That
> means we need to check the entity twice. If the entity isn't a task,

Does it really check it twice? Have you disassembled it to see if the code
is any better?

#define entity_is_task(se)	(!se->my_q)
static inline struct task_struct *task_of(struct sched_entity *se)
{
	SCHED_WARN_ON(!entity_is_task(se));
	return container_of(se, struct task_struct, se);
}

The above is a macro and a static inline, which means that the compiler
should optimized out that second check.


> return the task struct is meaningless.
> 
> Return NULL when entity isn't a task in task_of(), and call task_of()
> instead of entity_is_task() when we need a task_struct.

I'm not against the change, as it could be considered a clean up. But it is
up to the sched maintainers to decide if it's worth the churn.

-- Steve


> 
> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>

Re: [PATCH v2 1/2] sched/fair: Return NULL when entity isn't a task in task_of()

[Yajun Deng]

On 2024/1/23 11:48, Steven Rostedt wrote:
> On Wed,  6 Dec 2023 14:33:59 +0800
> Yajun Deng <yajun.deng@linux.dev> wrote:
>
>> Before calling task_of(), we need to make sure that the entity is a task.
>> There is also a warning in task_of() if the entity isn't a task. That
>> means we need to check the entity twice. If the entity isn't a task,
> Does it really check it twice? Have you disassembled it to see if the code
> is any better?
>
> #define entity_is_task(se)	(!se->my_q)
> static inline struct task_struct *task_of(struct sched_entity *se)
> {
> 	SCHED_WARN_ON(!entity_is_task(se));
> 	return container_of(se, struct task_struct, se);
> }
>
> The above is a macro and a static inline, which means that the compiler
> should optimized out that second check.


Yes, the second check should be optimized.

>
>> return the task struct is meaningless.
>>
>> Return NULL when entity isn't a task in task_of(), and call task_of()
>> instead of entity_is_task() when we need a task_struct.
> I'm not against the change, as it could be considered a clean up. But it is
> up to the sched maintainers to decide if it's worth the churn.


Return NULL in task_of() makes the code cleaner.

>
> -- Steve
>
>
>> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>