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Subject[tip:sched/core] sched/core: Introduce set_next_task() helper for better code readability
Commit-ID:  ff1cdc94de4d336be45336d70709dfcf3d682514
Gitweb: https://git.kernel.org/tip/ff1cdc94de4d336be45336d70709dfcf3d682514
Author: Muchun Song <smuchun@gmail.com>
AuthorDate: Fri, 26 Oct 2018 21:17:43 +0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Sun, 4 Nov 2018 00:59:24 +0100

sched/core: Introduce set_next_task() helper for better code readability

When we pick the next task, we will do the following for the task:

1) p->se.exec_start = rq_clock_task(rq);
2) dequeue_pushable(_dl)_task(rq, p);

When we call set_curr_task(), we also need to do the same thing
above. In rt.c, the code at 1) is in the _pick_next_task_rt()
and the code at 2) is in the pick_next_task_rt(). If we put two
operations in one function, maybe better. So, we introduce a new
function set_next_task(), which is responsible for doing the above.

By introducing the function we can get rid of calling the
dequeue_pushable(_dl)_task() directly(We can call set_next_task())
in pick_next_task() and have better code readability and reuse.
In set_curr_task_rt(), we also can call set_next_task().

Do this things such that we end up with:

static struct task_struct *pick_next_task(struct rq *rq,
struct task_struct *prev,
struct rq_flags *rf)
{
/* do something else ... */

put_prev_task(rq, prev);

/* pick next task p */

set_next_task(rq, p);

/* do something else ... */
}

put_prev_task() can match set_next_task(), which can make the
code more readable.

Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181026131743.21786-1-smuchun@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/deadline.c | 19 ++++++++++---------
kernel/sched/rt.c | 24 +++++++++++-------------
2 files changed, 21 insertions(+), 22 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 91e4202b0634..470ba6b464fe 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1695,6 +1695,14 @@ static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
}
#endif

+static inline void set_next_task(struct rq *rq, struct task_struct *p)
+{
+ p->se.exec_start = rq_clock_task(rq);
+
+ /* You can't push away the running task */
+ dequeue_pushable_dl_task(rq, p);
+}
+
static struct sched_dl_entity *pick_next_dl_entity(struct rq *rq,
struct dl_rq *dl_rq)
{
@@ -1750,10 +1758,8 @@ pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
BUG_ON(!dl_se);

p = dl_task_of(dl_se);
- p->se.exec_start = rq_clock_task(rq);

- /* Running task will never be pushed. */
- dequeue_pushable_dl_task(rq, p);
+ set_next_task(rq, p);

if (hrtick_enabled(rq))
start_hrtick_dl(rq, p);
@@ -1808,12 +1814,7 @@ static void task_fork_dl(struct task_struct *p)

static void set_curr_task_dl(struct rq *rq)
{
- struct task_struct *p = rq->curr;
-
- p->se.exec_start = rq_clock_task(rq);
-
- /* You can't push away the running task */
- dequeue_pushable_dl_task(rq, p);
+ set_next_task(rq, rq->curr);
}

#ifdef CONFIG_SMP
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index a21ea6021929..9aa3287ce301 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1498,6 +1498,14 @@ static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flag
#endif
}

+static inline void set_next_task(struct rq *rq, struct task_struct *p)
+{
+ p->se.exec_start = rq_clock_task(rq);
+
+ /* The running task is never eligible for pushing */
+ dequeue_pushable_task(rq, p);
+}
+
static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
struct rt_rq *rt_rq)
{
@@ -1518,7 +1526,6 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
static struct task_struct *_pick_next_task_rt(struct rq *rq)
{
struct sched_rt_entity *rt_se;
- struct task_struct *p;
struct rt_rq *rt_rq = &rq->rt;

do {
@@ -1527,10 +1534,7 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)
rt_rq = group_rt_rq(rt_se);
} while (rt_rq);

- p = rt_task_of(rt_se);
- p->se.exec_start = rq_clock_task(rq);
-
- return p;
+ return rt_task_of(rt_se);
}

static struct task_struct *
@@ -1573,8 +1577,7 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)

p = _pick_next_task_rt(rq);

- /* The running task is never eligible for pushing */
- dequeue_pushable_task(rq, p);
+ set_next_task(rq, p);

rt_queue_push_tasks(rq);

@@ -2355,12 +2358,7 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)

static void set_curr_task_rt(struct rq *rq)
{
- struct task_struct *p = rq->curr;
-
- p->se.exec_start = rq_clock_task(rq);
-
- /* The running task is never eligible for pushing */
- dequeue_pushable_task(rq, p);
+ set_next_task(rq, rq->curr);
}

static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
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